Farnesoid X receptor, hepatocyte nuclear factors 1α and 3β are essential for transcriptional activation of the liver-specific organic anion transporter-2 gene

Background. We isolated the human liver-specific organic anion transporter gene, LST-2 (OATP8/SLCO1B3), which is exclusively expressed in the basolateral membrane of the hepatocytes. In this study, we analyzed the transcriptional regulation of the LST-2 gene in hepatocyte-derived cells and the effect of bile acid. Methods. Transcriptional activity of the LST-2 gene was measured using a human LST-2 promoter-luciferase reporter plasmid under various concentrations of bile acids. Electrophoresis mobility shift assays of farnesoid X receptor (FXR), hepatocyte nuclear factor (HNF) 1 alpha, and HNF3 beta were performed. Results. Luciferase analysis showed that the 5'-flanking region from -180 to -20bp is responsible for LST-2 transcriptional activity. By site-directed mutation analysis, it was revealed that the consensus binding sites for FXR, HNF1 alpha, and HNF3 beta play important roles in the transcriptional activity of the LST-2 gene. By electrophoresis mobility shift assay, we observed specific protein-DNA complexes of FXR, HNF1 alpha, and HNF-3 beta. Luciferase activity was increased fivefold when chenodeoxycholate or deoxycholate were added. Northern blot analyses revealed that the expression of LST-2 was increased by addition of chenodeoxycholate or deoxycholate in a dose-dependent manner. Conclusions. This study demonstrated that the transcription of the LST-2 gene is regulated by three transcription factors, FXR, HNF1 alpha, and HNF3 beta. HNF1 alpha and HNF3 beta might contribute to its liver-specific expression, and FXR might play a role in its transcriptional activation by bile acids.