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Hepatocyte nuclear factor-4{alpha} and bile acids regulate human concentrative nucleoside transporter-1 gene expression


Klein, K; Kullak-Ublick, G A; Wagner, M; Trauner, M; Eloranta, J J (2009). Hepatocyte nuclear factor-4{alpha} and bile acids regulate human concentrative nucleoside transporter-1 gene expression. American Journal of Physiology. Gastrointestinal and Liver Physiology, 296(4):G936-G947.

Abstract

The concentrative nucleoside transporter-1 (CNT1) is a member of the solute carrier 28 (SLC28) gene family, and is expressed in the liver, intestine, and kidneys. CNT1 mediates the uptake of naturally occurring pyrimidine nucleosides, but also nucleoside analogues used in anticancer and antiviral therapy. Thus, expression levels of CNT1 may affect the pharmacokinetics of these drugs and the outcome of drug therapy. Because little is known about the transcriptional regulation of human CNT1 gene expression, we have characterized the CNT1 promoter with respect to DNA response elements and their binding factors. The transcriptional start site of the CNT1 gene was determined by 5'-RACE. In silico analysis revealed the existence of three putative binding sites for the nuclear receptor hepatocyte nuclear factor-4alpha (HNF-4alpha) within the CNT1 promoter. A luciferase reporter gene construct containing the CNT1 promoter region was transactivated by HNF-4alpha in human cell lines derived from the liver, intestine, and kidneys. Consistent with this, we showed in electromobility shift assays that HNF-4alpha specifically binds to two conserved direct repeat-1 (DR-1) motifs within the proximal CNT1 promoter. In cotransfection experiments, the transcriptional coactivator peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC-1alpha) further increased, whereas the bile acid-inducible corepressor small heterodimer partner (SHP) reduced, HNF-4alpha-dependent CNT1 promoter activity. Consistent with the latter phenomenon, CNT1 mRNA expression levels were suppressed in primary human hepatocytes upon bile acid treatment. Supporting the physiological relevance and species-conservation of this effect, ileal Cnt1 mRNA expression was decreased upon bile acid feeding and increased upon bile duct ligation in mice. Key words: nucleoside transport, bile acids, transcriptional regulation, nuclear receptors.

The concentrative nucleoside transporter-1 (CNT1) is a member of the solute carrier 28 (SLC28) gene family, and is expressed in the liver, intestine, and kidneys. CNT1 mediates the uptake of naturally occurring pyrimidine nucleosides, but also nucleoside analogues used in anticancer and antiviral therapy. Thus, expression levels of CNT1 may affect the pharmacokinetics of these drugs and the outcome of drug therapy. Because little is known about the transcriptional regulation of human CNT1 gene expression, we have characterized the CNT1 promoter with respect to DNA response elements and their binding factors. The transcriptional start site of the CNT1 gene was determined by 5'-RACE. In silico analysis revealed the existence of three putative binding sites for the nuclear receptor hepatocyte nuclear factor-4alpha (HNF-4alpha) within the CNT1 promoter. A luciferase reporter gene construct containing the CNT1 promoter region was transactivated by HNF-4alpha in human cell lines derived from the liver, intestine, and kidneys. Consistent with this, we showed in electromobility shift assays that HNF-4alpha specifically binds to two conserved direct repeat-1 (DR-1) motifs within the proximal CNT1 promoter. In cotransfection experiments, the transcriptional coactivator peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC-1alpha) further increased, whereas the bile acid-inducible corepressor small heterodimer partner (SHP) reduced, HNF-4alpha-dependent CNT1 promoter activity. Consistent with the latter phenomenon, CNT1 mRNA expression levels were suppressed in primary human hepatocytes upon bile acid treatment. Supporting the physiological relevance and species-conservation of this effect, ileal Cnt1 mRNA expression was decreased upon bile acid feeding and increased upon bile duct ligation in mice. Key words: nucleoside transport, bile acids, transcriptional regulation, nuclear receptors.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:04 Faculty of Medicine > University Hospital Zurich > Clinic for Clinical Pharmacology and Toxicology
04 Faculty of Medicine > Center for Integrative Human Physiology
Dewey Decimal Classification:570 Life sciences; biology
610 Medicine & health
Language:English
Date:April 2009
Deposited On:07 Apr 2009 10:08
Last Modified:05 Apr 2016 13:05
Publisher:American Physiological Society
ISSN:0193-1857
Free access at:Publisher DOI. An embargo period may apply.
Publisher DOI:https://doi.org/10.1152/ajpgi.90678.2008
PubMed ID:19228884
Permanent URL: https://doi.org/10.5167/uzh-16254

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