Toyono Takashi, Seta Yuji, Kataoka Shinji, Toyoshima Kuniaki
Division of Oral Histology and Neurobiology, Department of Biosciences, Science of Health Improvement, Kyushu Dental College, Kokurakita-ku, Kitakyushu 803-8580, Japan.
Biochim Biophys Acta. 2007 Nov-Dec;1769(11-12):641-8. doi: 10.1016/j.bbaexp.2007.08.003. Epub 2007 Sep 6.
The T1R family (T1R1, T1R2 and T1R3 receptors) has a role in the detection of umami and sweet tastes in taste buds. Although T1R3 is also expressed in the intrahepatic bile duct, the expression patterns of T1R1 and T1R2 in this region have not been determined. In addition, the mechanisms of transcriptional regulation of the human T1R3 gene (Tas1r3) have not been elucidated. In this study, we determined the expression patterns of T1R2 and T1R3 in human liver and the function of C/EBPbeta in Tas1r3 promoter activity. Immunohistochemistry showed that T1R2 and T1R3 were expressed in the intrahepatic bile duct. 5'-RACE analysis revealed that the transcriptional start sites of Tas1r3 were located 67 bp and 176 bp upstream of the ATG. Promoter analysis of Tas1r3 was performed using the luciferase reporter assay and EMSA in the Tas1r3-expressing cell line, HuCCT1. The 226-bp region upstream of the ATG had promoter activity, and C/EBPbeta activated the Tas1r3 promoter activity in HuCCT1 cells. These results show that T1R2 and T1R3 receptors, in addition to their role in taste perception, may also have a role in intrahepatic cholangiocytes. C/EBPbeta was identified as the transcription factor regulating Tas1r3 promoter activity in HuCCT1 cells.
T1R家族（T1R1、T1R2和T1R3受体）在味蕾中鲜味和甜味的检测中发挥作用。尽管T1R3也在肝内胆管中表达，但该区域中T1R1和T1R2的表达模式尚未确定。此外，人类T1R3基因（Tas1r3）的转录调控机制也尚未阐明。在本研究中，我们确定了T1R2和T1R3在人肝脏中的表达模式以及C/EBPβ在Tas1r3启动子活性中的功能。免疫组织化学显示T1R2和T1R3在肝内胆管中表达。5'-RACE分析表明Tas1r3的转录起始位点位于ATG上游67 bp和176 bp处。在表达Tas1r3的细胞系HuCCT1中，使用荧光素酶报告基因测定法和EMSA对Tas1r3进行启动子分析。ATG上游226 bp区域具有启动子活性，并且C/EBPβ在HuCCT1细胞中激活了Tas1r3启动子活性。这些结果表明，T1R2和T1R3受体除了在味觉感知中发挥作用外，在肝内胆管细胞中可能也具有作用。C/EBPβ被确定为在HuCCT1细胞中调节Tas1r3启动子活性的转录因子。
