WNK1-OSR1/SPAK KINASE CASCADE IS IMPORTANT FOR ANGIOGENESIS

WNK [with-no-lysine (K)] kinases are a family of four members of serine and threonine kinases that regulate renal Na⁺ and K⁺ transport. Mutations of WNK1 and WNK4 cause a hereditary hypertensive and hyperkalemic disease known as pseudohypoaldosteronism type II (PHA2). Unlike other WNK isoforms, WNK1 is ubiquitously expressed and regulates many other cellular processes outside the kidney. Oxidative stress response kinase (OSR1) and related STE 20/SPS1-related proline alanine-rich kinase (SPAK) are downstream kinases of WNK kinases. To examine the role of WNK kinase cascade in vivo, we generated global Wnk1-deleted mice and found that Wnk1-ablated mice die in utero from embryonic angiogenesis and cardiac developmental defects. Endothelial-specific Wnk1 deletion reveals that angiogenesis defect is due to WNK1 requirement in endothelium. We further showed that global and endothelial-deletion of Osr1 phenocopies Wnk1 deletion. Furthermore, expression of a catalytic constitutively active Osr1 transgene rescues angiogenesis defects and embryonic lethality of Wnk1-ablated mice. In zebrafish, Wnk1 knockdown causes similar angiogenesis defects to Vegf2 (Flk1) knockdown and that expression of WNK1 partially rescues Flk1 angiogenesis defects. The results indicate that WNK1 is downstream of VEGF signaling cascade. T-lymphocytes isolated from Wnk1-null mice exhibit migration defects. Inhibition of WNK1-OSR1 downstream target Na-K-2Cl cotransporter NKCC1 mimics migration defect of WNK1-deficient T-lymphocytes. Thus, WNK1-OSR1/SPAK cascade is important for angiogenesis. Regulation of ion homeostasis and cell volume may underlie the mechanism for WNK1 regulation of endothelial cell migration and angiogenesis.