A new kindred with pseudohypoaldosteronism type II and a novel mutation (564D>H) in the acidic motif of the WNK4 gene.
We identified a new kindred with the familial syndrome of hypertension and hyperkalemia (pseudohypoaldosteronism type II or Gordon's syndrome) containing an affected father and son. Mutation analysis confirmed a single heterozygous G to C substitution within exon 7 (1690G>C) that causes a missense mutation within the acidic motif of WNK4 (564D>H). We confirmed the function of this novel mutation by coexpressing it in Xenopus oocytes with either the NaCl cotransporter (NCCT) or the inwardly rectifying K-channel (ROMK). Wild-type WNK4 inhibits 22Na+ flux in Xenopus oocytes expressing NCCT by approximately 90% (P<0.001), whereas the 564D>H mutant had no significantly inhibitory effect on flux through NCCT. In oocytes expressing ROMK, wild-type WNK4 produced >50% inhibition of steady-state current through ROMK at a +20-mV holding potential (P<0.001). The 564D>H mutant produced further inhibition with steady-state currents to some 60% to 70% of those seen with the wild-type WNK4. Using fluorescent-tagged NCCT (enhanced cyan fluorescent protein-NCCT) and ROMK (enhanced green fluorescent protein-ROMK) to quantify the expression of the proteins in the oocyte membrane, it appears that the functional effects of the 564D>H mutation can be explained by alteration in the surface expression of NCCT and ROMK. Compared with wild-type WNK4, WNK4 564D>H causes increased cell surface expression of NCCT but reduced expression of ROMK. This work confirms that the novel missense mutation in WNK4, 564D>H, is functionally active and highlights further how switching charge on a single residue in the acid motif of WNK4 affects its interaction with the thiazide-sensitive target NCCT and the potassium channel ROMK.
Clinical Pharmacology Unit, University of Cambridge, United Kingdom.
Amir P
AP
Golbang
Meena
M
Murthy
Abbas
A
Hamad
Che-Hsiung
CH
Liu
Georgina
G
Cope
William
W
Van't Hoff
Alan
A
Cuthbert
Kevin M
KM
O'Shaughnessy
D000328:Adult; D020816:Amino Acid Motifs; D000818:Animals; D001224:Aspartic Acid; D002462:Cell Membrane / Q000378:metabolism; D005260:Female; D005820:Genetic Testing; D006639:Histidine; D006801:Humans; D006947:Hyperkalemia / Q000209:etiology; D006973:Hypertension / Q000209:etiology; D008297:Male; D020125:Mutation, Missense; D009865:Oocytes / Q000378:metabolism; D010375:Pedigree; D024661:Potassium Channels, Inwardly Rectifying / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics*; D011546:Pseudohypoaldosteronism / Q000150:complications / Q000235:genetics* / Q000503:physiopathology; D011955:Receptors, Drug / Q000378:metabolism; D049992:Sodium Chloride Symporters / Q000378:metabolism; D012979:Sodium Radioisotopes / Q000493:pharmacokinetics; D014982:Xenopus laevis
C086989:KCNJ1 protein, human; D024661:Potassium Channels, Inwardly Rectifying; D011955:Receptors, Drug; D049992:Sodium Chloride Symporters; D012979:Sodium Radioisotopes; C064415:thiazide receptor; D001224:Aspartic Acid; D006639:Histidine; D017346:Protein Serine-Threonine Kinases; C433806:WNK4 protein, human