Caractérisation structurale et fonctionnelle du facteur de transcription "hepatocyte nuclear factor-6"
(1999)
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- Abstract
- Tissue-specific transcription is regulated by transcription factors that are expressed only in a restricted number of tissues. Six families of hepatic transcription factors (HNF-1, HNF-3, HNF-4, HNF-6, C/EBP, PAR) control gene expression in liver. HNF-6 has been discovered in our laboratory. The aim of this work was to identify and to study the domains of HNF-6 that are involved in DNA-binding and in transcriptional stimulation. <BR> HNF-6 contains a single “cut” domain and a divergent homeodomain which is characterized by a phenylalanine at positron 48 and a methionine at position 50. There are two HNF-6 isoforms, HFN-6α (465 residues) and HNF-6β (491 residues). The latter is identical to HNF-6α, except for a longer linker region between the “cut” domain and the homeodomain. Our in vitro protein-DNA interaction studies (electrophoretic mobility shift assay) with HNF-6 deletion mutants show that the “cut” domain, the homeodomain and the linker region and on the nucleotide sequence of the target site. We also show that HNF-6 binds to DNA as a monomer. <BR> Our transient transfection experiments show that transcriptional stimulation by HNF-6 requires three domains, namely the “cut” domain, the homeodomain and a 24 residue-long serine/threonine/proline-rich region. The “cut” domain and the homeodomain of HNF-6 are therefore bifunctional: they are required for DNA-binding and transcriptional stimulation. To stimulate transcription, HNF-6 recruits coactivors, the identity of which depends on the sequence of the binding site. This recruitment involved both a LXXLL motif in the HNF-6 “cut” domain and the F48M50 dyad of the homeodomain. <BR> The structural characteristics of HNF-6 identify this factor as the founding member of a new class of homeoproteins, which we call ONECUT. Based in the knowledge of these characteristics we have cloned a new mammalian member of this class, which we call OC-2. The tissue distribution of CO-2 and its transcriptional activation properties in lifer differ from, but overlap with, those of HNF-6. <BR> We also show that HNF-6 is involved in the regulation of blood coagulation by stimulating the protein C gene promoter. Indeed, a mutation in this promoter that is associated with protein C deficiency leads to a loss of HNF-6 binding and action. <BR> In conclusion, the characterization of functional domains of HNF-6 led to the identification of a new class of homeoproteins and to the cloning of OC-2. The knowledge of the DNA-binding properties of HNF-6 also enable us to show that a human disease results from the loss of control of a gene by HNF-6. Finally, our functional data on HNF-6 and OC-2 suggest that these factors and their activators are involved in the network of hepatic transcription factors that is required for liver development and differentiation
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Lannoy, V. (1999). Caractérisation structurale et fonctionnelle du facteur de transcription “hepatocyte nuclear factor-6”. https://hdl.handle.net/2078.5/111044