Hou Jianghui, Renigunta Aparna, Konrad Martin, Gomes Antonio S, Schneeberger Eveline E, Paul David L, Waldegger Siegfried, Goodenough Daniel A
Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA.
J Clin Invest. 2008 Feb;118(2):619-28. doi: 10.1172/JCI33970.
Tight junctions (TJs) play a key role in mediating paracellular ion reabsorption in the kidney. Familial hypomagnesemia with hypercalciuria and nephrocalcinosis (FHHNC) is an inherited disorder caused by mutations in the genes encoding the TJ proteins claudin-16 (CLDN16) and CLDN19; however, the mechanisms underlying the roles of these claudins in mediating paracellular ion reabsorption in the kidney are not understood. Here we showed that in pig kidney epithelial cells, CLDN19 functioned as a Cl(-) blocker, whereas CLDN16 functioned as a Na(+) channel. Mutant forms of CLDN19 that are associated with FHHNC were unable to block Cl(-) permeation. Coexpression of CLDN16 and CLDN19 generated cation selectivity of the TJ in a synergistic manner, and CLDN16 and CLDN19 were observed to interact using several criteria. In addition, disruption of this interaction by introduction of FHHNC-causing mutant forms of either CLDN16 or CLDN19 abolished their synergistic effect. Our data show that CLDN16 interacts with CLDN19 and that their association confers a TJ with cation selectivity, suggesting a mechanism for the role of mutant forms of CLDN16 and CLDN19 in the development of FHHNC.
紧密连接（TJs）在介导肾脏细胞旁离子重吸收中起关键作用。家族性低镁血症伴高钙尿症和肾钙质沉着症（FHHNC）是一种遗传性疾病，由编码紧密连接蛋白claudin - 16（CLDN16）和CLDN19的基因突变引起；然而，这些claudin蛋白在介导肾脏细胞旁离子重吸收中所起作用的潜在机制尚不清楚。在此我们表明，在猪肾上皮细胞中，CLDN19起到Cl⁻阻滞剂的作用，而CLDN16起到Na⁺通道的作用。与FHHNC相关的CLDN19突变形式无法阻止Cl⁻通透。CLDN16和CLDN19的共表达以协同方式产生紧密连接的阳离子选择性，并且通过多种标准观察到CLDN16和CLDN19相互作用。此外，引入导致FHHNC的CLDN16或CLDN19突变形式破坏这种相互作用，消除了它们的协同效应。我们的数据表明CLDN16与CLDN19相互作用，并且它们的结合赋予紧密连接阳离子选择性，这提示了CLDN16和CLDN19突变形式在FHHNC发生发展中作用的一种机制。
