Hepatocyte nuclear factor-6 stimulates transcription of the alpha-fetoprotein gene and synergizes with the retinoic-acid-receptor-related orphan receptor alpha-4.
The rat alpha-fetoprotein ( afp ) gene is controlled by three enhancers whose function depends on their interaction with liver-enriched transcription factors. The afp enhancer III, located at -6 kb, is composed of three regions that act in synergy. Two of these regions, called s1 and s2, contain a putative binding site for hepatocyte nuclear factor-6 (HNF-6). This factor is the prototype of the ONECUT family of cut-homoeodomain proteins and is a known regulator of liver gene expression in adults and during development. We show here that the two splicing isoforms of HNF-6 bind to a site in the s1 region and in the s2 region. The core sequence of the s1 site corresponds to none of the known HNF-6 binding sites. Nevertheless, the binding properties of the s1 site are identical with those of the s2 site and of previously characterized HNF-6 binding sequences. The HNF-6 consensus should therefore be rewritten as DRRTCVATND. Binding of HNF-6 to the s1 and s2 sites requires both the cut and the homoeo domains, is co-operative and induces DNA bending. HNF-6 strongly stimulates the activity of the afp enhancer III in transient transfection experiments. This effect requires the stereo-specific alignment of the two HNF-6 sites. Moreover, HNF-6 stimulates the enhancer in synergy with the retinoic-acid-receptor-related orphan receptor alpha (RORalpha), which binds to a neighbouring site in the s1 region. Thus expression of the afp gene requires functional interactions between HNF-6 molecules and between HNF-6 and RORalpha.
Nacer-Cherif
Habib
H
Centre de Recherche sur l'Endocrinologie Moléculaire et le Développement, CNRS UPR 9078, 9 rue Jules Hetzel, F 92190 Meudon, France.
Bois-Joyeux
Brigitte
B
Rousseau
Guy G
GG
Lemaigre
Frédéric P
FP
Danan
Jean-Louis
JL
D017398:Alternative Splicing; D000818:Animals; D001665:Binding Sites; D006528:Carcinoma, Hepatocellular / Q000235:genetics; D004247:DNA / Q000378:metabolism; D004742:Enhancer Elements, Genetic; D051559:Hepatocyte Nuclear Factor 6; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008113:Liver Neoplasms / Q000235:genetics; D057094:Nuclear Receptor Subfamily 1, Group F, Member 1; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism*; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured; D000509:alpha-Fetoproteins / Q000235:genetics* / Q000378:metabolism
D051559:Hepatocyte Nuclear Factor 6; D018398:Homeodomain Proteins; D057094:Nuclear Receptor Subfamily 1, Group F, Member 1; C496605:ONECUT1 protein, human; C539738:RORA protein, human; D018160:Receptors, Cytoplasmic and Nuclear; D015534:Trans-Activators; D000509:alpha-Fetoproteins; D004247:DNA