Ishibashi K, Kuwahara M, Gu Y, Tanaka Y, Marumo F, Sasaki S
Second Department of Internal Medicine, Tokyo Medical and Dental University, Japan.
Biochem Biophys Res Commun. 1998 Mar 6;244(1):268-74. doi: 10.1006/bbrc.1998.8252.
A new member (AQP9) of the aquaporin family was identified from human leukocytes by homology cloning using PCR. A full length clone was obtained by screening human liver cDNA library. AQP9 encodes a 295-amino-acid protein with the amino acid sequence identity with AQP3 (48%), AQP7 (45%), and other aquaporins (approximately 30%), suggesting that AQP3, AQP7, and AQP9 belong to a subfamily of the aquaporin family. Injection of AQP9-cRNA into Xenopus oocytes stimulated the osmotic water permeability 7-folds with a low activation energy (4.2 kcal/mol) which was inhibited by 0.3 mM mercury chloride by 48%. AQP9 also facilitated urea transport 4-folds. However, in contrast to AQP3 and AQP7, AQP9 did not stimulate the glycerol permeability, suggesting a unique permeability character. Northern blot analysis revealed the high expression of 3.5-kb messages in peripheral leukocytes >> liver > lung = spleen, but not in thymus. The possible role of AQP9 in the immunological function of leukocytes is intriguing and the identification of AQP9 with unique permeability profile may expand our understanding of water and small solute transport in the body.
通过聚合酶链反应（PCR）同源克隆，从人白细胞中鉴定出一种水通道蛋白家族的新成员（AQP9）。通过筛选人肝脏cDNA文库获得了全长克隆。AQP9编码一种295个氨基酸的蛋白质，其氨基酸序列与AQP3的一致性为48%，与AQP7的一致性为45%，与其他水通道蛋白的一致性约为30%，这表明AQP3、AQP7和AQP9属于水通道蛋白家族的一个亚家族。将AQP9-cRNA注射到非洲爪蟾卵母细胞中，可使渗透水通透性提高7倍，且活化能较低（4.2千卡/摩尔），0.3毫摩尔氯化汞可使其降低48%。AQP9还能使尿素转运增加4倍。然而，与AQP3和AQP7不同的是，AQP9不会刺激甘油通透性，这表明其具有独特的通透性特征。Northern印迹分析显示，在外周血白细胞中3.5千碱基的信使RNA高表达 >> 肝脏 > 肺 = 脾脏，但在胸腺中不表达。AQP9在白细胞免疫功能中的可能作用很有趣，且具有独特通透性特征的AQP9的鉴定可能会扩展我们对体内水和小溶质转运的理解。
