Second Affiliated Hospital, Wenzhou Medical College, Zhejiang, China.
J Am Soc Nephrol. 2010 Jan;21(1):82-92. doi: 10.1681/ASN.2008121275. Epub 2009 Oct 29.
WNK kinase is a serine/threonine kinase that plays an important role in electrolyte homeostasis. WNK4 significantly inhibits the surface expression of the sodium chloride co-transporter (NCC) by enhancing the degradation of NCC through a lysosomal pathway, but the mechanisms underlying this trafficking are unknown. Here, we investigated the effect of the lysosomal targeting receptor sortilin on NCC expression and degradation. In Cos-7 cells, we observed that the presence of WNK4 reduced the steady-state amount of NCC by approximately half. Co-transfection with truncated sortilin (a dominant negative mutant) prevented this WNK4-induced reduction in NCC. NCC immunoprecipitated with both wild-type sortilin and, to a lesser extent, truncated sortilin. Immunostaining revealed that WNK4 increased the co-localization of NCC with the lysosomal marker cathepsin D, and NCC co-localized with wild-type sortilin, truncated sortilin, and WNK4 in the perinuclear region. These findings suggest that WNK4 promotes NCC targeting to the lysosome for degradation via a mechanism involving sortilin.
丝氨酸/苏氨酸激酶 WNK 是一种在电解质稳态中发挥重要作用的激酶。WNK4 通过增强通过溶酶体途径的 NCC 的降解，显著抑制氯化钠共转运蛋白（NCC）的表面表达，但这种运输的机制尚不清楚。在这里，我们研究了溶酶体靶向受体 sortilin 对 NCC 表达和降解的影响。在 Cos-7 细胞中，我们观察到 WNK4 的存在使 NCC 的稳态量减少了大约一半。与截断的 sortilin（显性负突变体）共转染可防止这种 WNK4 诱导的 NCC 减少。WNK4 与野生型 sortilin 和（在较小程度上）截断的 sortilin 一起免疫沉淀 NCC。免疫染色显示，WNK4 增加了 NCC 与溶酶体标记物组织蛋白酶 D 的共定位，并且 NCC 与野生型 sortilin、截断的 sortilin 和核周区域中的 WNK4 共定位。这些发现表明，WNK4 通过涉及 sortilin 的机制促进 NCC 靶向溶酶体进行降解。
