Disclosures: All authors state that they have no conflicts of interest.
Hepatocyte Nuclear Factor 4α (HNF4α) in Coordination With Retinoic Acid Receptors Increases all-trans-Retinoic Acid-Dependent CYP26A1 Gene Expression in HepG2 Human Hepatocytes
Article first published online: 13 AUG 2014
© 2014 Wiley Periodicals, Inc.
Journal of Cellular Biochemistry
Volume 115, Issue 10, pages 1740–1751, October 2014
How to Cite
Zolfaghari, R. and Ross, A. C. (2014), Hepatocyte Nuclear Factor 4α (HNF4α) in Coordination With Retinoic Acid Receptors Increases all-trans-Retinoic Acid-Dependent CYP26A1 Gene Expression in HepG2 Human Hepatocytes. J. Cell. Biochem., 115: 1740–1751. doi: 10.1002/jcb.24839
Authors' contribution: Study design, conduct, data interpretation and manuscript preparation: RZ and ACR. Study design, data and manuscript review: ACR. Both authors take responsibility for the integrity of the data analysis.
- Issue published online: 13 AUG 2014
- Article first published online: 13 AUG 2014
- Accepted manuscript online: 12 MAY 2014 06:52AM EST
- Manuscript Accepted: 8 MAY 2014
- Manuscript Revised: 11 APR 2014
- Manuscript Received: 6 FEB 2014
- TRANSCRIPTION FACTOR;
- RETINOIC ACID RESPONSE ELEMENT;
- LIVER-SPECIFIC GENE EXPRESSION
CYP26A1 expression is very highly induced by retinoic acid (RA) in the liver, compared to most other tissues, suggesting that a liver-enriched factor may be required for its physiological transcriptional response. HNF4α is a highly conserved liver-specific/enriched member of nuclear receptor superfamily. In this study, we hypothesized that HNF4α and RARs may cooperate in an RA-dependent manner to induce a high level of CYP26A1 expression in liver cells. Partial inhibition of endogenous HNF4α by siRNA reduced the level of RA-induced CYP26A1 mRNA in HepG2 cells. Cotransfection of HNF4α, with or without RARs, demonstrated RA-dependent activation of a human CYP26A1 promoter-luciferase construct. Analysis of a 2.5-kbp putative CYP26A1 promoter sequence identified five potential HNF4α DNA response elements: H1 located in a proximal region overlapping with an RAR element-1 (RARE1 or R1); H2 and H3 in the distal region, close to RARE2 (R2) and RARE3 (R3); and H4 and H5 in intermediary regions. In EMSA and ChIP analyses HNF4α and RARs binding in the proximal and distal CYP26A1 promoter regions was significantly higher in RA-treated cells. Mutational analysis of the individual HNF4α DNA-response elements identified H1 as the major site for HNF4α binding because mutation of H1 inhibited the promoter activity by ~90%, followed by H2 mutation with less than 40% inhibition. Our results indicate that HNF4α coordinates with RARs in an RA-dependent manner to strongly induce CYP26A1 gene expression in the liver, which may explain the high level of response to RA observed in vivo. J. Cell. Biochem. 115: 1740–1751, 2014. © 2014 Wiley Periodicals, Inc.