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Catalytic domain of the Serine/Threonine protein kinase, With No Lysine (WNK) 4 STKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine residues on protein substrates. WNK4 shows a restricted expression pattern and is usually found in epithelial cells. It is expressed in nephrons and in extrarenal tissues including intestine, eye, mammary glands, and prostate. WNK4 regulates a variety of ion transport proteins including apical or basolateral ion transporters, ion channels in the transcellular pathway, and claudins in the paracellular pathway. Mutations in WNK4 cause PseudoHypoAldosteronism type II (PHAII), characterized by hypertension and hyperkalemia. WNK4 inhibits the activity of the thiazide-sensitive Na-Cl cotransporter (NCC), which is responsible for about 15% of NaCl reabsorption in the kidney. It also inhibits the renal outer medullary potassium channel (ROMK) and decreases its surface expression. Hypertension and hyperkalemia in PHAII patients with WNK4 mutations may be partly due to increased NaCl reabsorption through NCC and impaired renal potassium secretion by ROMK, respectively. The WNK4 subfamily is part of a larger superfamily that includes the catalytic domains of other protein STKs, protein tyrosine kinases, RIO kinases, aminoglycoside phosphotransferase, choline kinase, and phosphoinositide 3-kinase. |
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