Sodium Chloride Cotransporter Regulation by WNK Kinase

描述（由申请人提供）： WNK（不含赖氨酸（K））是一种新发现的丝氨酸/苏氨酸激酶亚家族，参与控制上皮细胞的离子渗透性。发现WNK 1和WNK 4激酶的突变可引起假性醛固酮减少症II型（PHA II），也称为戈登综合征。PHA II是一种罕见的常染色体显性遗传疾病，以高血压、高钾血症和代谢性酸中毒为特征。其临床特征可通过噻嗪类利尿剂（一种氯化钠协同转运蛋白（NCC）抑制剂）逆转。免疫荧光研究和北方印迹分析表明，WNK 1和WNK 4都存在于参与氯离子转运的各种极化上皮细胞中，如肾脏、阵挛性隐窝、汗管、胰管、胆管、附睾和大脑的室管膜。导致PHA II的WNK激酶突变表明WNK激酶参与远端肾单位对氯化钠处理的调节。最近的研究表明，WNK 4对非洲爪蟾卵母细胞中NCC活性和NCC表面表达的抑制作用，进一步证明WNK 4激酶通过直接或间接机制调节NCC功能。本研究拟探讨WNK 4激酶在肾小管细胞NCC调控中的作用。待检验的假设是WNK 4激酶的不适当靶向和/或功能将通过改变NCC加工直接影响NCC调节和/或通过改变哺乳动物细胞中NCC的磷酸化间接影响NCC调节。这一假设得到了强有力的初步数据的支持，即NCC的表面表达被WNK 4显著降低。相比之下，NCC表面表达不受非洲绿色猴肾（Cos-7）细胞中WNK 4突变体的影响。进一步研究WNK 4对NCC的调控将为理解WNK 4激酶的生理作用提供重要信息，并有助于确定PHA II的潜在机制，这些机制对于更好地理解原发性高血压的发病机制至关重要。

DESCRIPTION (provided by applicant): WNKs (with no lysine (K)) are a newly described novel subfamily of serine/threonine kinases implicated in controlling the ionic permeability of epithelia. Mutations in WNK1 and WNK4 kinases are found to cause pseudohypoaldosteronism type II (PHA II), also referred to as Gordon syndrome. PHA II is a rare autosomal dominant disorder featuring hypertension, hyperkalemia and metabolic acidosis. Its clinical features are reversed by a thiazide diuretic, a sodium chloride cotransporter (NCC) inhibitor. Immunofluorescent studies and Northern blot analysis demonstrated that both WNK1 and WNK4 are present in a variety of polarized epithelia involved in chloride ion transport, such as kidney, clonic crypts, sweat ducts, pancreatic ducts, biliary ducts, epididymis and the ependyma of the brain. Mutations in WNK kinases resulting in PHA II suggest that WNK kinase is involved in the regulation of sodium chloride handling by the distal nephron. Recent studies have shown an inhibitory effect of WNK4 on NCC activity and surface expression of NCC in Xenopus oocytes, further demonstrating that WNK4 kinase regulates NCC function through direct or indirect mechanisms. This research proposal is to examine the role of WNK4 kinase in NCC regulation in the renal tubular cells. The hypothesis to be tested is that inappropriate targeting and/or function of the WNK4 kinase will affect NCC regulation directly by altering the NCC processing and/or indirectly by altering the phosphorylation of NCC in mammalian cells. This hypothesis is supported by strong preliminary data that surface expression of NCC is significantly reduced by WNK4. In contrast, NCC surface expression is unaffected by WNK4 mutants in African green monkey kidney (Cos-7) cells. Further investigating the regulation of NCC by WNK4 will provide important information to understanding the physiological role of WNK4 kinase and help to identify the underlying mechanisms of PHA II that are crucial in better understanding the pathogenesis of essential hypertension.