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

Abstract

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 HNF1a expression was downregulated with small interfering RNA. Following HNF1a overexpression in Huh7 cells, the intron 1 ECR increased SV40 promoter activity by 11-fold and OCT1 promoter activity by 6-fold. Without HNF1a 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 5 0.48, P 5 0.002, n 5 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.

Genetic Variants in Transcription Factors Are Associated With the Pharmacokinetics and Pharmacodynamics of Metformin

“…Activating enhancer binding protein (AP)2 has been shown to have a repressive effect on MATE1 gene expression 3 , 28 , 30 . Other transcription factors have also been linked to modulating the expression levels of OCTs and MATEs involved in metformin disposition 7 , 9 , 27 , 29 , 31 , 32 . To date, the impact of transcription factor polymorphisms on metformin PK and response phenotypes has not been studied.…”

“…3,28,30 Other transcription factors have also been linked to modulating the expression levels of OCTs and MATEs involved in metformin disposition. 7,9,27,29,31,32 To date, the impact of transcription factor polymorphisms on metformin PK and response phenotypes has not been studied. Our hypothesis is that, compared with genetic variants in transporter genes, genetic variants in transcription factors may have a stronger impact on overall metformin plasma and tissue levels.…”

PharmGKB summary

“…Hepatocyte nuclear factor 1 may be an even stronger regulator of SLC22A1 in the human liver, as high HNF1 expression is significantly correlated with high OCT1 expression in human liver samples. Further, electrophoretic mobility shift and chromatin immunoprecipitation assays confirmed the specific binding of HNF1 to the intron 1 evolutionary conserved region of SLC22A1 [11]. In addition, the ubiquitously expressed and constitutively active transcriptional factor USF1 was shown to bind to the proximal promoter region and to modulate the basal expression of OCT1 [12].…”

OCT1 Genetic Variants are Associated with Postoperative Morphine-Related Adverse Effects in Children

“…However, there is no report on contribution of different SNPs of OCT1 on clinical outcomes/adverse effects of morphine. Four loss of function OCT1 variants have been reported before: Arg61Cys (rs12208357), Cys88Arg (rs55918055), Gly401Ser (rs34130495) and Gly465Arg (rs34059508), and change of Met420 (rs72552763) amino acids [20,21]. Tzvetkov et al [19] showed in vitro studies that morphine uptake was increased up to fourfold in HEK293 cells overexpressing human OCT1.…”