Kikuchi Ryota, Kusuhara Hiroyuki, Hattori Naka, Kim Insook, Shiota Kunio, Gonzalez Frank J, Sugiyama Yuichi
Department of Molecular Pharmacokinetics, Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
Mol Pharmacol. 2007 Dec;72(6):1619-25. doi: 10.1124/mol.107.039701. Epub 2007 Sep 13.
Expression of Urate transporter 1 (URAT1/SLC22A12) is restricted to the proximal tubules in the kidney, where it is responsible for the tubular reabsorption of urate. To elucidate the mechanism underlying its tissue-specific expression, the transcriptional regulation of the hURAT1 and mUrat1 genes was investigated. Hepatocyte nuclear factor 1 alpha (HNF1alpha) and HNF1beta positively regulate minimal promoter activity of the URAT1 gene as shown by reporter gene assays. Electrophoretic mobility shift assays revealed binding of HNF1alpha and/or HNF1beta to the HNF1 motif in the hURAT1 promoter. Furthermore, the mRNA expression of Urat1 is reduced in the kidneys of Hnf1alpha-null mice compared with wild-type mice, confirming the indispensable role of HNF1alpha in the constitutive expression of URAT1 genes. It was also shown that the proximal promoter region of mUrat1 was hypermethylated in the liver and kidney medulla, whereas this region was relatively hypomethylated in the kidney cortex. These methylation profiles are in a good agreement with the proximal tubule-restricted expression of mUrat1 in the kidney cortex. Taken together, these results strongly suggest that tissue-specific expression of the URAT1 genes is coordinately regulated by the transcriptional activation by HNF1alpha/HNF1beta heterodimer and repression by DNA methylation.
尿酸转运蛋白1（URAT1/SLC22A12）的表达仅限于肾脏近端小管，在那里它负责尿酸的肾小管重吸收。为了阐明其组织特异性表达的潜在机制，研究了hURAT1和mUrat1基因的转录调控。报告基因检测显示，肝细胞核因子1α（HNF1α）和HNF1β正向调节URAT1基因的最小启动子活性。电泳迁移率变动分析揭示了HNF1α和/或HNF1β与hURAT1启动子中的HNF1基序结合。此外，与野生型小鼠相比，Hnf1α基因敲除小鼠肾脏中Urat1的mRNA表达降低，证实了HNF1α在URAT1基因组成型表达中的不可或缺作用。研究还表明，mUrat1的近端启动子区域在肝脏和肾髓质中高度甲基化，而在肾皮质中该区域甲基化程度相对较低。这些甲基化谱与mUrat1在肾皮质近端小管的限制性表达高度一致。综上所述，这些结果强烈表明，URAT1基因的组织特异性表达受HNF1α/HNF1β异二聚体的转录激活和DNA甲基化抑制的协同调控。
