Mulders S M, Knoers N V, Van Lieburg A F, Monnens L A, Leumann E, Wühl E, Schober E, Rijss J P, Van Os C H, Deen P M
Department of Cell Physiology, University of Nijmegen, The Netherlands.
J Am Soc Nephrol. 1997 Feb;8(2):242-8. doi: 10.1681/ASN.V82242.
Nephrogenic diabetes insipidus (NDI) is characterized by the inability of the kidney to concentrate urine in response to vasopressin. The autosomal recessive form of NDI is caused by mutations in the AQP2 gene, encoding the vasopressin-regulated water channel of the kidney collecting duct. This report presents three new mutations in the AQP2 gene that cause NDI, resulting in A147T-, T126M-, or N68S-substituted AQP2 proteins. Expression of the A147T and T126M mutant AQP2 proteins in Xenopus oocytes revealed a relatively small, but significant increase in water permeability, whereas the water permeability of N68S expressing oocytes was not increased. cRNA encoding missense and wild-type AQP2 were equally stable in oocytes. Immunoblots of oocyte lysates showed that only the A147T mutant protein was less stable than wild-type AQP2. The mutant AQP2 proteins showed, in addition to the wild-type 29-kd band, an endoplasmic reticulum-retarded form of AQP2 of approximately 32 kd. Immunoblotting and immunocytochemistry demonstrated only intense labeling of the plasma membranes of oocytes expressing wild-type AQP2. In summary, two mutant AQP2 proteins encoded in NDI are functional water channels. Therefore, the major cause underlying autosomal recessive NDI is the misrouting of AQP2 mutant proteins.
肾性尿崩症（NDI）的特征是肾脏无法对血管加压素作出反应而浓缩尿液。NDI的常染色体隐性形式是由AQP2基因突变引起的，该基因编码肾集合管中受血管加压素调节的水通道。本报告介绍了导致NDI的AQP2基因中的三个新突变，产生了A147T、T126M或N68S替代的AQP2蛋白。在非洲爪蟾卵母细胞中表达A147T和T126M突变型AQP2蛋白显示水通透性有相对较小但显著的增加，而表达N68S的卵母细胞的水通透性没有增加。编码错义突变和野生型AQP2的cRNA在卵母细胞中同样稳定。卵母细胞裂解物的免疫印迹显示只有A147T突变蛋白比野生型AQP2更不稳定。除了野生型29-kd条带外，突变型AQP2蛋白还显示出一种约32 kd的内质网滞留形式的AQP2。免疫印迹和免疫细胞化学仅显示表达野生型AQP2的卵母细胞质膜有强烈标记。总之，NDI中编码的两种突变型AQP2蛋白是功能性水通道。因此，常染色体隐性NDI的主要原因是AQP2突变蛋白的错误定位。
