title: Angiotensin II signaling increases activity of the renal Na-Cl cotransporter through a WNK4-SPAK-dependent pathway.
abstract: Mutations in the kinase WNK4 cause pseudohypoaldosteronism type II (PHAII), a syndrome featuring hypertension and high serum K(+) levels (hyperkalemia). WNK4 has distinct functional states that regulate the balance between renal salt reabsorption and K(+) secretion by modulating the activities of renal transporters and channels, including the Na-Cl cotransporter NCC and the K(+) channel ROMK. WNK4's functions could enable differential responses to intravascular volume depletion (hypovolemia) and hyperkalemia. Because hypovolemia is uniquely associated with high angiotensin II (AngII) levels, AngII signaling might modulate WNK4 activity. We show that AngII signaling in Xenopus oocytes increases NCC activity by abrogating WNK4's inhibition of NCC but does not alter WNK4's inhibition of ROMK. This effect requires AngII, its receptor AT1R, and WNK4, and is prevented by the AT1R inhibitor losartan. NCC activity is also increased by WNK4 harboring mutations found in PHAII, and this activity cannot be further augmented by AngII signaling, consistent with PHAII mutations providing constitutive activation of the signaling pathway between AT1R and NCC. AngII's effect on NCC is also dependent on the kinase SPAK because dominant-negative SPAK or elimination of the SPAK binding motif in NCC prevent activation of NCC by AngII signaling. These effects extend to mammalian cells. AngII increases phosphorylation of specific sites on SPAK and NCC that are necessary for activation of each in mpkDCT cells. These findings place WNK4 in the signaling pathway between AngII and NCC, and provide a mechanism by which hypovolemia maximizes renal salt reabsoprtion without concomitantly increasing K(+) secretion.
authors.affiliation: Molecular Physiology Unit, Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán, Universidad Nacional Autónoma de México, Tlalpan 14000 Mexico City, Mexico.
authors.forename: Pedro
authors.initials: P
authors.lastname: San-Cristobal
authors.forename: Diana
authors.initials: D
authors.lastname: Pacheco-Alvarez
authors.forename: Ciaran
authors.initials: C
authors.lastname: Richardson
authors.forename: Aaron M
authors.initials: AM
authors.lastname: Ring
authors.forename: Norma
authors.initials: N
authors.lastname: Vazquez
authors.forename: Fatema H
authors.initials: FH
authors.lastname: Rafiqi
authors.forename: Divya
authors.initials: D
authors.lastname: Chari
authors.forename: Kristopher T
authors.initials: KT
authors.lastname: Kahle
authors.forename: Qiang
authors.initials: Q
authors.lastname: Leng
authors.forename: Norma A
authors.initials: NA
authors.lastname: Bobadilla
authors.forename: Steven C
authors.initials: SC
authors.lastname: Hebert
authors.forename: Dario R
authors.initials: DR
authors.lastname: Alessi
authors.forename: Richard P
authors.initials: RP
authors.lastname: Lifton
authors.forename: Gerardo
authors.initials: G
authors.lastname: Gamba
mesh_terms: D000804:Angiotensin II / Q000378:metabolism*; D000818:Animals; D006947:Hyperkalemia; D006973:Hypertension; D020896:Hypovolemia; D007668:Kidney / Q000378:metabolism*; D051379:Mice; D009865:Oocytes; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D015398:Signal Transduction; D049992:Sodium Chloride Symporters / Q000378:metabolism*; D014162:Transfection; D014981:Xenopus
chemical_list: D049992:Sodium Chloride Symporters; D000804:Angiotensin II; D017346:Protein Serine-Threonine Kinases; C486409:STK39 protein, human; C433806:WNK4 protein, human