Cation-coupled chloride cotransporters (CCC) play a role in modulating intracellular chloride concentration ([Cl⁻]_i) and cell volume. Cell shrinkage and cell swelling are accompanied by an increase or decrease in [Cl⁻]_i, respectively. Cell shrinkage and a decrease in [Cl⁻]_i increase the activity of NKCCs (Na-K-Cl cotransporters: NKCC1, NKCC2, and Na-Cl) and inhibit the activity of KCCs (K-Cl cotransporters: KCC1 to KCC4), wheras cell swelling and an increase in [Cl⁻]_i activate KCCs and inhibit NKCCs; thus, it is unlikely that the same kinase is responsible for both effects. WNK1 and WNK4 are chloride-sensitive kinases that modulate the activity of CCC in response to changes in [Cl⁻]_i. Here, we showed that WNK3, another member of the serine-threonine kinase WNK family with known effects on CCC, is not sensitive to [Cl⁻]_i but can be regulated by changes in extracellular tonicity. In contrast, WNK4 is highly sensitive to [Cl⁻]_i but is not regulated by changes in cell volume. The activity of WNK3 toward NaCl cotransporter is not affected by eliminating the chloride-binding site of WNK3, further confirming that the kinase is not sensitive to chloride. Chimeric WNK3/WNK4 proteins were produced, and analysis of the chimeras suggests that sequences within the WNK’s carboxy-terminal end may modulate the chloride affinity. We propose that WNK3 is a cell volume-sensitive kinase that translates changes in cell volume into phosphorylation of CCC.

中文翻译：

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WNK3 和 WNK4 对细胞体积和细胞内氯化物浓度表现出相反的敏感性。

阳离子偶联氯离子协同转运蛋白 (CCC) 在调节细胞内氯离子浓度 ([Cl ^- ] _i ) 和细胞体积方面发挥作用。细胞收缩和细胞膨胀分别伴随着[Cl ^- ] _i的增加或减少。细胞收缩和在下降[氯^- ]_我增加NKCCs（钠-K-CL协同转运蛋白：NKCC1，NKCC2，和Na-Cl）的活性和抑制的KCC的活性（K-CL协同转运蛋白：KCC1到KCC4），鉴于细胞肿胀和 [Cl ^- ] _{i 增加}激活 KCCs 并抑制 NKCCs；因此，同一种激酶不太可能导致这两种效应。WNK1 和 WNK4 是氯敏感激酶，可响应 [Cl ^- ] _{i 的}变化调节 CCC 的活性。在这里，我们表明 WNK3，丝氨酸 - 苏氨酸激酶 WNK 家族的另一个成员，对 CCC 具有已知的影响，对 [Cl ^- ] _i不敏感，但可以通过细胞外张力的变化进行调节。相比之下，WNK4 对 [Cl ^- ] _i高度敏感但不受细胞体积变化的调节。WNK3 对 NaCl 协同转运蛋白的活性不受消除 WNK3 的氯化物结合位点的影响，进一步证实该激酶对氯化物不敏感。产生了嵌合 WNK3/WNK4 蛋白，对嵌合体的分析表明 WNK 羧基末端内的序列可能会调节氯化物亲和力。我们提出 WNK3 是一种细胞体积敏感激酶，可将细胞体积的变化转化为 CCC 的磷酸化。