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Publication : An SGK1 site in WNK4 regulates Na+ channel and K+ channel activity and has implications for aldosterone signaling and K+ homeostasis.

First Author  Ring AM Year  2007
Journal  Proc Natl Acad Sci U S A Volume  104
Issue  10 Pages  4025-9
PubMed ID  17360471 Mgi Jnum  J:248255
Mgi Id  MGI:6093077 Doi  10.1073/pnas.0611728104
Citation  Ring AM, et al. (2007) An SGK1 site in WNK4 regulates Na+ channel and K+ channel activity and has implications for aldosterone signaling and K+ homeostasis. Proc Natl Acad Sci U S A 104(10):4025-9
abstractText  The steroid hormone aldosterone is secreted both in the setting of intravascular volume depletion and hyperkalemia, raising the question of how the kidney maximizes NaCl reabsorption in the former state while maximizing K(+) secretion in the latter. Mutations in WNK4 cause pseudohypoaldosteronism type II (PHAII), a disease featuring increased renal NaCl reabsorption and impaired K(+) secretion. PHAII-mutant WNK4 achieves these effects by increasing activity of the Na-Cl cotransporter (NCC) and the Na(+) channel ENaC while concurrently inhibiting the renal outer medullary K(+) channel (ROMK). We now describe a functional state for WNK4 that promotes increased, rather than decreased, K(+) secretion. We show that WNK4 is phosphorylated by SGK1, a mediator of aldosterone signaling. Whereas wild-type WNK4 inhibits the activity of both ENaC and ROMK, a WNK4 mutation that mimics phosphorylation at the SGK1 site (WNK4(S1169D)) alleviates inhibition of both channels. The net result of these effects in the kidney would be increased K(+) secretion, because of both increased electrogenic Na(+) reabsorption and increased apical membrane K(+) permeability. Thus, modification at the PHAII and SGK1 sites in WNK4 impart opposite effects on K(+) secretion, decreasing or increasing ROMK activity and net K(+) secretion, respectively. This functional state for WNK4 would thus promote the desired physiologic response to hyperkalemia, and the fact that it is induced downstream of aldosterone signaling implicates WNK4 in the physiologic response to aldosterone with hyperkalemia. Together, the different states of WNK4 allow the kidney to provide distinct and appropriate integrated responses to intravascular volume depletion and hyperkalemia.
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