| Co-Investigator(Kenkyū-buntansha) |
KATAYOSE Yu TOHOKU UNIVERSITY, HOSPITAL, RESEARCH ASSOCIATE, 病院・助手 (20302151)
ABE Takaaki TOHOKU UNIVERSITY, HOSPITAL, LECTOR, 病院・講師 (80292209)
UNNO Michiaki TOHOKU UNIVERSITY, HOSPITAL, LECTOR, 病院・講師 (70282043)
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| Research Abstract |
The basolateral membrane of the hepatocyte is characterized by various transporters, one of which is responsible for cellular uptake of organic anionic substances, including bile acids, steroids and certain drugs from the blood. We have isolated human liver-specific organic anion transporter, LST-2 (SLC21A8, OATP8), which is exclusively expressed in the basolateral membrane of the hepatocyte. We demonstrated that LST-2 transports chenodeoxycholate, which is a ligand for the farnesoid X receptor (FXR). In this study, we analyzed the transcriptional regulation of the LST-2 gene in hepatocyte-derived cells. We also examined the effect of bile acid on LBT-2 gene transcription. The promoter activity of the 5'-upstream region of the LST-2 gene was analyzed by luciferase reporter gene assay. Deletion analysis showed that the 5'-flanking region from -180 to -20 bp is responsible for LST-2 transcriptional activity. By site-directed mutation analysis, it was revealed that the consensus binding sites for FXR, HNF1a, and HNF3b 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, HRF1a, and HNF3b. Luciferase activity was increased 5-fold when chenodeoxycholate or deoxycholate were added but was not increased using the vector mutated at the FXR binding site. Western blot and northern blot analyses revealed that the expression of LST-2 was increased by addition of chenodeoxycholate or deoxycholate were in a dose-dependent manner. In conclusion, our findings suggest that HNF1a and HNF3b might contribute to liver-specific expression and FXR might play a role in transcriptional activation by chenodeoxycholate and deoxycholate.
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