Cytokine regulation of the liver transcription factor hepatocyte nuclear factor-3β is mediated by the C/EBP family and interferon regulatory factor 1

Three distinct hepatocyte nuclear factor-3 (HNF-3) proteins (α, β, and γ) regulate the transcription of numerous liver-enriched genes. The HNF-3 proteins bind DNA via a homologous winged helix motif common to a number of proteins known to be critical for determination events in embryogenesis. We have demonstrated previously that two binding sites in the -184 HNF-3β promoter are recognized by widely distributed factors and that there is also a critical autoregulatory site present that is recognized by members of the HNF-3 family. Adjacent to the autoregulatory site, we identified a binding site for a cell-specific factor, LF-H3β, that may function in restricting HNF-3β gene expression to hepatocytes. Our present study demonstrates that members of the C/EBP and proline and acidic amino acid-rich subfamilies of basic region leucine zipper transcription factors bind the LF-H3β site, and cotransfection of HepG2 cells shows that these factors are able to activate an HNF-3β promoter reporter construct. The LF-H3β-C/EBP binding sequence also confers HNF-3β promoter stimulation in response to interleukin (IL)-1 and IL-6. Upstream of this HNF-3β proximal promoter region, an IFN- stimulated response element core sequence (-231 to -210) was found that mediates transcriptional induction by IFN-γ but not IFN-α. Gel mobility supershift assay demonstrates that an IFN-γ-induced protein-DNA complex is disrupted by an antibody specific for interferon regulatory factor- 1/interferon-stimulated gene factor-2. Consistent with this finding, we observed that IFN-γ induction requires ongoing protein synthesis. Surprisingly, the effect of the three cytokines (IL-1, IL-6, and IFN-γ) in combination as assayed by the same model is not synergistic. HNF-3β joins the C/EBP family on the list of liver-enriched transcription factors, the expression of which is modulated by cytokines.