WNK4

WNK4, a serine/threonine kinase lacking a catalytic lysine, functions as a key regulator of electrolyte transport in the distal nephron^[1][2]. It modulates the activity of epithelial ion channels and transporters, including the thiazide-sensitive Na⁺-Cl^- cotransporter (NCC) and the renal outer medullary potassium channel (ROMK), influencing both chloride reabsorption and potassium secretion^[3][4][5]. Mechanistically, WNK4 inhibits NCC by promoting its lysosomal degradation but can switch to a stimulatory role under angiotensin II signaling or in the presence of kidney-specific WNK1 isoforms (KS-WNK1), which activate WNK4 via protein-protein interactions without changing intracellular chloride^[4][6][7]. WNK4 also regulates TRPV4 and BK channel surface expression through pathways involving ERK and p38 MAPK, highlighting its role in renal osmosensing and potassium homeostasis^[8][9]. Disease relevance is evidenced by familial hyperkalemic hypertension (FHHt), where WNK4 mutations disrupt transporter regulation, causing salt-sensitive hypertension and hyperkalemia^[1][10][5]. Compared with related isoforms, WNK4 exhibits unique COOH-terminal coiled-coil and degron motifs that enable differential interactions with KLHL3/2, distinguishing it from WNK1, WNK2, and WNK3 in substrate specificity and oligomerization^[11][12]. Experimental applications include the use of ATP-competitive inhibitors such as WNK463, which target WNK4 with isoform-specific binding and phosphorylation-dependent conformational stabilization, providing tools for dissecting kinase signaling in renal physiology and hypertension models^[13][12].