WNK4 regulates activity of the epithelial Na+ channel in vitro and in vivo.
Homeostasis of intravascular volume, Na(+), Cl(-), and K(+) is interdependent and determined by the coordinated activities of structurally diverse mediators in the distal nephron and the distal colon. The behavior of these flux pathways is regulated by the renin-angiotensin-aldosterone system; however, the mechanisms that allow independent modulation of individual elements have been obscure. Previous work has shown that mutations in WNK4 cause pseudohypoaldosteronism type II (PHAII), a disease featuring hypertension with hyperkalemia, due to altered activity of specific Na-Cl cotransporters, K(+) channels, and paracellular Cl(-) flux mediators of the distal nephron. By coexpression studies in Xenopus oocytes, we now demonstrate that WNK4 also inhibits the epithelial Na(+) channel (ENaC), the major mediator of aldosterone-sensitive Na(+) (re)absorption, via a mechanism that is independent of WNK4's kinase activity. This inhibition requires intact C termini in ENaC beta- and gamma-subunits, which contain PY motifs used to target ENaC for clearance from the plasma membrane. Importantly, PHAII-causing mutations eliminate WNK4's inhibition of ENaC, thereby paralleling other effects of PHAII to increase sodium balance. The relevance of these findings in vivo was studied in mice harboring PHAII-mutant WNK4. The colonic epithelium of these mice demonstrates markedly increased amiloride-sensitive Na(+) flux compared with wild-type littermates. These studies identify ENaC as a previously unrecognized downstream target of WNK4 and demonstrate a functional role for WNK4 in the regulation of colonic Na(+) absorption. These findings support a key role for WNK4 in coordinating the activities of diverse flux pathways to achieve integrated fluid and electrolyte homeostasis.
Ring
Aaron M
AM
Departments of Genetics, Medicine, and Molecular Biophysics and Biochemistry, Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT 06510, USA.
Cheng
Sam X
SX
Leng
Qiang
Q
Kahle
Kristopher T
KT
Rinehart
Jesse
J
Lalioti
Maria D
MD
Volkman
Heather M
HM
Wilson
Frederick H
FH
Hebert
Steven C
SC
Lifton
Richard P
RP
D000450:Aldosterone / Q000378:metabolism; D000818:Animals; D003106:Colon / Q000378:metabolism; D053503:Epithelial Sodium Channels / Q000378:metabolism*; D006947:Hyperkalemia / Q000378:metabolism; D006973:Hypertension / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D009154:Mutation; D009865:Oocytes / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics* / Q000502:physiology*; D011546:Pseudohypoaldosteronism / Q000378:metabolism; D051381:Rats; D012084:Renin-Angiotensin System; D014982:Xenopus laevis / Q000378:metabolism
D053503:Epithelial Sodium Channels; D000450:Aldosterone; C499024:Prkwnk4 protein, mouse; D017346:Protein Serine-Threonine Kinases