Department of Internal Medicine, Washington University Renal Division, Washington University, St Louis, MO, USA.
EMBO J. 2012 Apr 18;31(8):1999-2012. doi: 10.1038/emboj.2012.49. Epub 2012 Feb 28.
The paracellular claudin channel of the thick ascending limb (TAL) of Henle is critical for Ca(++) reabsorption in the kidney. Genome-wide association studies (GWASs) have identified claudin-14 associated with hypercalciuric nephrolithiasis. Here, we show that claudin-14 promoter activity and transcript are exclusively localized in the TAL. Under normal dietary condition, claudin-14 proteins are suppressed by two microRNA molecules (miR-9 and miR-374). Both microRNAs directly target the 3'-UTR of claudin-14 mRNA; induce its mRNA decay and translational repression in a synergistic manner. Through physical interaction, claudin-14 blocks the paracellular cation channel made of claudin-16 and -19, critical for Ca(++) reabsorption in the TAL. The transcript and protein levels of claudin-14 are upregulated by high Ca(++) diet, while downregulated by low Ca(++) diet. Claudin-14 knockout animals develop hypermagnesaemia, hypomagnesiuria, and hypocalciuria under high Ca(++) dietary condition. MiR-9 and miR-374 transcript levels are regulated by extracellular Ca(++) in a reciprocal manner as claudin-14. The Ca(++) sensing receptor (CaSR) acts upstream of the microRNA-claudin-14 axis. Together, these data have established a key regulatory role for claudin-14 in renal Ca(++) homeostasis.
密蛋白-14 构成的细胞旁通道在肾脏钙重吸收中起关键作用。全基因组关联研究（GWAS）已发现密蛋白-14 与钙结石性肾病相关。本文研究表明，密蛋白-14 启动子活性和转录本仅定位于 Henle 升支粗段（TAL）。在正常饮食条件下，两种 microRNA 分子（miR-9 和 miR-374）抑制密蛋白-14 蛋白。这两种 microRNA 均可直接靶向密蛋白-14 mRNA 的 3'-UTR；以协同方式诱导其 mRNA 降解和翻译抑制。密蛋白-14 通过物理相互作用，阻断由密蛋白-16 和 -19 构成的细胞旁阳离子通道，该通道对 TAL 中的钙重吸收至关重要。高钙饮食上调密蛋白-14 的转录本和蛋白水平，而低钙饮食则下调其表达。高钙饮食条件下，密蛋白-14 敲除动物出现高镁血症、尿镁排泄减少和尿钙排泄减少。miR-9 和 miR-374 的转录本水平受细胞外钙以相互反式方式调控，与密蛋白-14 相反。钙敏感受体（CaSR）作为 microRNA-密蛋白-14 轴的上游因子。综上所述，这些数据确立了密蛋白-14 在肾脏钙稳态中的关键调节作用。
