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The organic cation transporter 1 (OCT1), also known as solute carrier family 22 member 1, is strongly and specifically expressed in the human liver. Here we show that the hepatocyte nuclear factor 1 (HNF1) regulates OCT1 transcription and contributes to the strong, liver-specific expression of OCT1. Bioinformatic analyses revealed strong conservation of HNF1 binding motifs in an evolutionary conserved region (ECR) in intron 1 of the OCT1 gene. Electrophoretic mobility shift and chromatin immunoprecipitation assays confirmed the specific binding of HNF1 to the intron 1 ECR. In reporter gene assays performed in HepG2 cells, the intron 1 ECR increased SV40 promoter activity by 22-fold and OCT1 promoter activity by 13-fold. The increase was reversed when the HNF1 binding sites in the intron 1 ECR were mutated or the endogenous HNF1α expression was downregulated with small interfering RNA. Following HNF1α overexpression in Huh7 cells, the intron 1 ECR increased SV40 promoter activity by 11-fold and OCT1 promoter activity by 6-fold. Without HNF1α overexpression, the increases were only 3- and 2-fold, respectively. Finally, in human liver samples, high HNF1 expression was significantly correlated with high OCT1 expression (r = 0.48, P = 0.002, n = 40). In conclusion, HNF1 is a strong regulator of OCT1 expression. It remains to be determined whether genetic variants, disease conditions, or drugs that affect HNF1 activity may affect the pharmacokinetics and efficacy of OCT1-transported drugs such as morphine, tropisetron, ondansetron, tramadol, and metformin. Beyond OCT1, this study demonstrates the validity and usefulness of interspecies comparisons in the discovery of functionally relevant genomic sequences.

the journal of pharmacology and experimental therapeutics/the journal of pharmacology and experimental therapeutics

Hepatocyte Nuclear Factor 1 Regulates the Expression of the Organic Cation Transporter 1 via Binding to an Evolutionary Conserved Region in Intron 1 of the <i>OCT1</i> Gene

Hepatocyte Nuclear Factor 1 Regulates the Expression of the Organic Cation Transporter 1 via Binding to an Evolutionary Conserved Region in Intron 1 of the OCT1 Gene