Ohta Akihito, Yang Sung-Sen, Rai Tatemitsu, Chiga Motoko, Sasaki Sei, Uchida Shinichi
Department of Nephrology, Graduate School of Medicine, Tokyo Medical and Dental University, Tokyo 113-8519, Japan.
Biochem Biophys Res Commun. 2006 Oct 20;349(2):804-8. doi: 10.1016/j.bbrc.2006.08.101. Epub 2006 Aug 24.
Pseudohypoaldosteronism type II (PHAII), an autosomal dominant disorder characterized by hypertension, hyperkalemia, and hyperchloremic acidosis, is reportedly due to mutations in WNK1 and WNK4 kinase genes. However, the pathogenesis of the disease remains unknown. Mutations in the WNK1 gene are the deletions in the first intron, which reportedly increases WNK1 mRNA expression. Thus, we generated WNK1 over-expressing stable cell lines using MDCKII cells to model the distal nephron of PHAII patients. Using these cell lines, we investigated whether increased WNK1 expression might affect paracellular chloride permeability and claudin phosphorylation, since we previously observed an increase in both with a disease-causing mutant WNK4. WNK1 expression in MDCKII cells increased chloride permeability two to threefold. Co-expression of wild-type WNK4 did not further increase WNK1-enhanced chloride permeability. WNK1 expression also induced phosphorylation of endogenous claudin-4 in MDCKII cells, as well as over-expressed claudin-4. Combined, these results suggest that increased WNK1 expression has the same effect on chloride permeability and claudin phosphorylation as the mutant WNK4. Thus, increased chloride shunt may be involved in the pathogenesis of PHAII caused by WNK1 mutations.
II型假性醛固酮增多症（PHAII）是一种常染色体显性疾病，其特征为高血压、高钾血症和高氯性酸中毒，据报道是由WNK1和WNK4激酶基因突变所致。然而，该疾病的发病机制仍不清楚。WNK1基因的突变是第一内含子的缺失，据报道这会增加WNK1 mRNA的表达。因此，我们利用MDCKII细胞构建了WNK1过表达稳定细胞系，以模拟PHAII患者的远端肾单位。利用这些细胞系，我们研究了WNK1表达增加是否会影响细胞旁氯离子通透性和紧密连接蛋白的磷酸化，因为我们之前观察到致病突变型WNK4会使二者均增加。MDCKII细胞中WNK1的表达使氯离子通透性提高了两到三倍。野生型WNK4的共表达并未进一步增加WNK1增强的氯离子通透性。WNK1的表达还诱导了MDCKII细胞内源性紧密连接蛋白-4以及过表达的紧密连接蛋白-4的磷酸化。综合这些结果表明，WNK1表达增加对氯离子通透性和紧密连接蛋白磷酸化的影响与突变型WNK4相同。因此，氯离子分流增加可能参与了由WNK1突变引起的PHAII的发病机制。
