WNK-SPAK-NCC Cascade Revisited WNK1 Stimulates the Activity of the Na-Cl Cotransporter via SPAK, an Effect Antagonized by WNK4

The with-no-lysine (K) kinases, WNK 1 and WiNK4, are key regulators of blood pressure. Their mutations lead to familial hyperkalemic hypertension (FIII It), associated with an activation of the Na-Cl cotransporter (NCC). Although it is clear that WNK4 mutants activate NCC via S te20 proline-alaninc rich kinasc, the mechanisms responsible for WNK1-related Fl II It and alterations in NCC activity are not as clear, We tested whether WNK1 modulates NCC through WNK4, as predicted by some models, by crossing our recently developed WNK1-FHHt mice (WNK1(+/FHHt)) with WNK4(-/-) mice. Surprisingly, the activated NCC, hypertension, and hyperkalemia of WNK1(+FHHt) mice remain in the absence of WNK4. We demonstrate that WNK1 powerfully stimulates NCC in a WNK4-independent and Ste20 prolinc-alanine rich kinase dependent manner. Moreover, WNK4 decreases the WNK1 and WNK3-mediated activation of NCC. Finally, the formation of oligomers of WNK kinases through their C-terminal coiled-coil domain is essential for their activity toward NCC. In conclusion, WNK kinases form a network in which WNK4 associates with WNK1 and WNK3 to regulate NCC.