CCAAT/Enhancer-binding protein β regulates expression of human T1R3 taste receptor gene in the bile duct carcinoma cell line, HuCCT1

The T1R family (T1R1, T I 1R2 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 (Taslr3) have not been elucidated. In this study, we determined the expression patterns of T1R2 and TIR3 in human liver and the function of C/EBP beta in Taslr3 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 Tas lr3 were located 67. bp and 176 bp upstream of the ATG. Promoter analysis of Taslr3 was performed using the luciferase reporter assay and EMSA in the Taslr3-expressing cell line, HuCCT1 The 226-bp region upstream of the ATG had promoter activity, and C/EBP beta activated the Taslr3 promoter activity in HuCCT1 cells. These results show that T1R2 and TIR3 receptors, in addition to their role in taste perception, may also have a role in intrahepatic cholangiocytes. C/EBP was identified as the transcription factor regulating Taslr3 promoter activity in HuCCT1 cells. (c) 2007 Elsevier B.V. All rights reserved.