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J Biol Chem. 2001 Oct 5;276(40):37206-14. Epub 2001 Aug 1.

Characterization of the human OATP-C (SLC21A6) gene promoter and regulation of liver-specific OATP genes by hepatocyte nuclear factor 1 alpha.

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Division of Clinical Pharmacology and Toxicology, University Hospital, CH-8091 Zurich, Switzerland .


OATP-C (SLC21A6) is the predominant Na(+)-independent uptake system for bile salts and bilirubin of human liver and is expressed exclusively at the basolateral (sinusoidal) hepatocyte membrane. To investigate the basis of liver-specific expression of OATP-C, we studied promoter function in the two hepatocyte-derived cell lines HepG2 and Huh7 and in nonhepatic HeLa cells. OATP-C promoter constructs containing from 66 to 950 nucleotides of 5'-regulatory sequence were active in HepG2 and Huh7 but not HeLa cells, indicating that determinants of hepatocyte-specific expression reside within the minimal promoter. Deoxyribonuclease I footprint analysis revealed a single region that was protected by HepG2 and Huh7 but not HeLa cell nuclear extracts. The liver-enriched transcription factor hepatocyte nuclear factor 1 alpha (HNF1 alpha) was shown by mobility shift assays to bind within this footprint. Coexpression of HNF1 alpha stimulated OATP-C promoter activity 30-fold in HepG2 and 49-fold in HeLa cells. Mutation of the HNF1 site abolished promoter function, indicating that HNF1 alpha is critical for hepatocyte-specific OATP-C gene expression. The human OATP8 (SLC21A8) and mouse Oatp4 (Slc21a6) promoters were also responsive to HNF1 alpha coexpression in HepG2 cells. These data support a role for HNF1 alpha as a global regulator of liver-specific bile salt and organic anion transporter genes.

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