Hepatocyte Nuclear Factor 4α (HNF4α) in Coordination With Retinoic Acid Receptors Increases all‐trans‐Retinoic Acid‐Dependent CYP26A1 Gene Expression in HepG2 Human Hepatocytes

Abstract

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.

Impact of Retinoic Acid on Immune Cells and Inflammatory Diseases

“…RA can also signal through peroxisome proliferator-activating receptor beta (PPAR- β ) when it forms a heterodimer with RXR, which may be important for lipid metabolism and glucose homeostasis [ 1 ]. In addition, chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII) [ 32 ] and hepatocyte nuclear factor 4 (HNF-4) [ 33 ] receptors can forms a heterodimer with RXR and become low-affinity retinoic acid receptors. Similar to PPAR- β , their signals are important for lipid metabolism and glucose homeostasis [ 32 ].…”

Role of Hepatocyte Nuclear Factor 4α in Regulating Hepatic Differentiation and the Inflammatory Response in HCC

“…Of interest, studies have shown that retinoic acid, ginsenoside Rg3 and 18β-glycyrrhetinic acid can induce hepatic differentiation at least partly via modulation of HNF 4α [41][42][43]. These findings suggest that it should be possible to induce differentiation in HCC.…”

Innovation for hepatotoxicity in vitro research models: A review

“…HNF4α plays important roles in lipid and glucose metabolism, and in the catabolism of xenobiotics and drugs, particularly by CYP450 (Hwang‐Verslues & Sladek, ; Jover, Bort, Gomez‐Lechon, & Castell, ). Zolfaghari and Ross found that HNF4α combined with retinoic acid enhanced expression of CYP26A1 (Zolfaghari & Ross, ). HNF6 can relieve hepatic apoptosis and impede the progression of liver disease, and has distinct mechanisms to enhance hepatic protection (Wang, ).…”

“…These transcription factors constitute a complex regulatory network that accurately controls liver development and hepatocyte function(Bingle, Hackett, Moxley, Longmore, & Gitlin, 1995;Colclough, Bellanne-Chantelot, Saint-Martin, Flanagan, & Ellard, 2013;Hajarnis et al, 2015).With the help of HNFs, such as HNF4α, HNF6 and HNF1α, in vitro models provide a more accurate determination of DMEs.HNF4α plays important roles in lipid and glucose metabolism, and in the catabolism of xenobiotics and drugs, particularly by CYP450(Hwang-Verslues & Sladek, 2010;Jover, Bort, Gomez-Lechon, & Castell, 2001). Zolfaghari and Ross found that HNF4α combined with retinoic acid enhanced expression of CYP26A1(Zolfaghari & Ross, 2014). HNF6 can relieve hepatic apoptosis and impede the progression of liver disease, and has distinct mechanisms to enhance hepatic…”