Department of Physiology, Shandong University School of Medicine, Jinan 250012, PR China.
Biochem Biophys Res Commun. 2011 Jan 28;404(4):979-84. doi: 10.1016/j.bbrc.2010.12.095. Epub 2010 Dec 25.
With-no-lysine (K) kinase 4 (WNK4) is a protein serine/threonine kinase associated with a Mendelian form of hypertension. WNK4 is an integrative regulator of renal transport of Na(+), K(+), and Cl(-) as shown in Xenopus oocyte system. In addition, WNK4 enhances the surface expression of epithelial Ca(2+) channel TRPV5, which plays a key role in the fine tuning of renal Ca(2+) reabsorption. Variations in the magnitude of WNK4-mediated regulation on TRPV5 in Xenopus oocytes suggest additional cellular components with limited expression are required for the regulation. In this study, we identified the Na(+)/H(+) exchanger regulating factor 2 (NHERF2) as a critical component for the positive regulation of TRPV5 by WNK4. NHERF2 augmented the positive effect of WNK4 on TRPV5, whereas its homolog NHERF1 had no effect when tested in the Xenopus oocyte system. The C-terminal PDZ binding motif of TRPV5 was required for the regulation by NHERF2. While NHERF2 interacted with TRPV5, no association between NHERF2 and WNK4 was detected using a GST pull-down assay. WNK4 increased the forward trafficking of TRPV5; however, it also caused an accelerated decline of the functional TRPV5 channels at later stage of co-expression. NHERF2 stabilized TRPV5 at the plasma membrane without interrupting the forward trafficking of TRPV5, thus prevented the decline of functional TRPV5 channel caused by WNK4 at later stage. The complementary and orderly regulations of WNK4 and NHERF2 allow TRPV5 functions at higher level for a longer period to maximize Ca(2+) influx.
无赖氨酸 (K) 激酶 4 (WNK4) 是一种丝氨酸/苏氨酸蛋白激酶，与一种孟德尔形式的高血压有关。WNK4 是 Na(+)、K(+)和 Cl(-)在 Xenopus 卵母细胞系统中的肾转运的综合调节剂。此外，WNK4 增强了上皮钙通道 TRPV5 的表面表达，这在肾钙重吸收的精细调节中起着关键作用。WNK4 在 Xenopus 卵母细胞中对 TRPV5 的调节幅度的变化表明，需要具有有限表达的其他细胞成分进行调节。在这项研究中，我们确定了钠/氢交换调节因子 2 (NHERF2) 是 WNK4 对 TRPV5 正调节的关键组成部分。NHERF2 增强了 WNK4 对 TRPV5 的正向作用，而当其在 Xenopus 卵母细胞系统中进行测试时，其同源物 NHERF1 没有作用。TRPV5 的 C 端 PDZ 结合基序是 NHERF2 调节所必需的。虽然 NHERF2 与 TRPV5 相互作用，但使用 GST 下拉测定未检测到 NHERF2 与 WNK4 之间的关联。WNK4 增加了 TRPV5 的正向转运；然而，在共表达的后期阶段，它也导致功能性 TRPV5 通道的功能迅速下降。NHERF2 在质膜上稳定 TRPV5，而不会中断 TRPV5 的正向转运，从而防止 WNK4 在后期阶段引起功能性 TRPV5 通道的下降。WNK4 和 NHERF2 的互补和有序调节允许 TRPV5 在更高水平更长时间地发挥作用，以最大限度地增加 Ca(2+)内流。
