Smith C P, Lee W S, Martial S, Knepper M A, You G, Sands J M, Hediger M A
Department of Medicine, Brigham and Women's Hospital, Boston, Massachussetts 02115, USA.
J Clin Invest. 1995 Sep;96(3):1556-63. doi: 10.1172/JCI118194.
In mammals, urea is the predominant end-product of nitrogen metabolism and plays a central role in the urinary-concentrating mechanism. Urea accumulation in the renal medulla is critical to the ability of the kidney to concentrate urine to an osmolality greater than systemic plasma. Regulation of urea excretion and accumulation in the renal medulla depends on the functional state of specialized phloretin-sensitive urea transporters. To study these transporters and their regulation of expression we isolated a cDNA which encodes the rat homologue (rUT2) of rabbit UT2 (You, G., C.P. Smith, Y. Kanai, W.-S. Lee, M. Stelzner, and M.A. Hediger, et al. Nature (Lond.). 1993. 365:844-847). Rat UT2 has 88% amino acid sequence identity to rabbit UT2 and 64% identity to the recently cloned human erythrocyte urea transporter, HUT11 (Olives, B., P. Neav, P. Bailly, M.A. Hediger, G. Rousselet, J.P. Cartron, and P. Ripoch J. Biol. Chem. 1994. 269:31649-31652). Analysis of rat kidney mRNA revealed two transcripts of size 2.9 and 4.0 kb which had spatially distinct distributions. Northern analysis and in situ hybridization showed that the 4.0-kb transcript was primarily responsive to changes in the protein content of the diet whereas the 2.9-kb transcript was responsive to changes in the hydration state of the animal. These studies reveal that the expression levels of the two rUT2 transcripts are modulated by different pathways to allow fluid and nitrogen balance to be regulated independently. Our data provide important insights into the regulation of the renal urea transporter UT2 and provide a basis on which to refine our understanding of the urinary concentrating mechanism and its regulation.
在哺乳动物中，尿素是氮代谢的主要终产物，在尿液浓缩机制中起核心作用。尿素在肾髓质中的蓄积对于肾脏将尿液浓缩至高于全身血浆渗透压的能力至关重要。尿素在肾髓质中的排泄和蓄积调节取决于专门的根皮素敏感尿素转运体的功能状态。为了研究这些转运体及其表达调控，我们分离出了一个编码大鼠兔UT2同源物（rUT2）的cDNA（You, G., C.P. Smith, Y. Kanai, W.-S. Lee, M. Stelzner, and M.A. Hediger, et al. Nature (Lond.). 1993. 365:844-847）。大鼠UT2与兔UT2具有88%的氨基酸序列同一性，与最近克隆的人类红细胞尿素转运体HUT11具有64%的同一性（Olives, B., P. Neav, P. Bailly, M.A. Hediger, G. Rousselet, J.P. Cartron, and P. Ripoch J. Biol. Chem. 1994. 269:31649-31652）。对大鼠肾脏mRNA的分析显示有两种大小分别为2.9 kb和4.0 kb的转录本，它们具有空间上不同的分布。Northern分析和原位杂交表明，4.0 kb的转录本主要对饮食中蛋白质含量的变化有反应，而2.9 kb的转录本对动物水合状态的变化有反应。这些研究表明，两种rUT2转录本的表达水平通过不同途径进行调节，以使液体和氮平衡能够独立调节。我们的数据为肾尿素转运体UT2的调节提供了重要见解，并为完善我们对尿液浓缩机制及其调节的理解提供了基础。
