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(Hypertension. 2005;46:295.)
© 2005 American Heart Association, Inc.
Original Articles |
From the Clinical Pharmacology Unit, and the Department of Medicine (M.M., A.C.), University of Cambridge, United Kingdom; and NephroUrology Unit, Great Ormond Street Hospital, London, United Kingdom (W.V.H.).
Correspondence to Dr K.M. OShaughnessy, Clinical Pharmacology Unit Level 6, ACCI Box 110, Addenbrookes Hospital Cambridge, CB2 2QQ, UK. E-mail kmo22{at}medschl.cam.ac.uk
We identified a new kindred with the familial syndrome of hypertension and hyperkalemia (pseudohypoaldosteronism type II or Gordons 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
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 proteinNCCT) and ROMK (enhanced green fluorescent proteinROMK) 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.
Key Words: kinase mutation
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