Mutations in WNK1 and WNK4
kinase genes have been shown to cause a human hereditary hypertensive disease,
pseudohypoaldosteronism type II (PHAII). We previously discovered that WNK
kinases phosphorylate and activate OSR1/SPAK
kinases that regulate renal SLC12A family transporters such as NKCC2 and NCC, and clarified that the constitutive activation of this cascade causes PHAII. WNK3, another member of the WNK
kinase family, was reported to be a strong activator of NCC/NKCC2 when assayed in Xenopus oocytes, suggesting that WNK3 also plays a major role in regulating blood pressure and
sodium reabsorption in the kidney. However, it remains to be determined whether WNK3 is in fact involved in the regulation of these transporters in vivo. To clarify this issue, we generated and analyzed WNK3 knockout mice. Surprisingly, phosphorylation and expression of OSR1, SPAK, NKCC2 and NCC did not decrease in knockout mouse kidney under normal and
low-salt diets. Similarly, expression of epithelial Na channel and
Na/H exchanger 3 were not affected in knockout mice. Na(+) and K(+) excretion in urine in WNK3 knockout mice was not affected under different
salt diets. Blood pressure in WNK3 knockout mice was not lower under normal diet. However, lower blood pressure was observed in WNK3 knockout mice fed
low-salt diet. WNK4 and WNK1 expression was slightly elevated in the knockout mice under
low-salt diet, suggesting compensation for WNK3 knockout by these WNKs. Thus, WNK3 may have some role in the WNK-OSR1/SPAK-NCC/NKCC2 signal cascade in the kidney, but its contribution to total WNK
kinase activity may be minimal.