Developmentally regulated N-terminal variants of the nuclear receptor hepatocyte nuclear factor 4alpha mediate multiple interactions through coactivator and corepressor-histone deacetylase complexes.
To understand the mechanisms governing the regulation of nuclear receptor (NR) function, we compared the parameters of activation and repression of two isoforms of the orphan receptor hepatocyte nuclear factor (HNF) 4alpha. HNF4alpha7 and HNF4alpha1 differ only in their N-terminal domains, and their expression in the liver is regulated developmentally. We show that the N-terminal activation function (AF)-1 of HNF4alpha1 possesses significant activity that can be enhanced through interaction with glucocorticoid receptor-interacting protein 1 (GRIP-1) and cAMP response element-binding protein-binding protein (CBP). In striking contrast, HNF4alpha7 possesses no measurable AF-1, implying major functional differences between the isoforms. Indeed, although HNF4alpha1 and HNF4alpha7 are able to interact via AF-2 with GRIP-1, p300, and silencing mediator for retinoid and thyroid receptors (SMRT), only HNF4alpha1 interacts in a synergistic fashion with GRIP-1 and p300. Although both isoforms interact physically and functionally with SMRT, the repression of HNF4alpha7 is less robust than that of HNF4alpha1, which may be caused by an increased ability of the latter to recruit histone deacetylase (HDAC) activity to target promoters. Moreover, association of SMRT with HDACs enhanced recruitment of HNF4alpha1 but not of HNF4alpha7. These observations suggest that NR isoform-specific association with SMRT could affect activity of the SMRT complex, implying that selection of HDAC partners is a novel point of regulation for NR activity. Possible physiological consequences of the multiple interactions with these coregulators are discussed.
Torres-Padilla
Maria Elena
ME
Unité de Génétique de la Différenciation, FRE 2364 du CNRS, Département de Biologie du Développement, Institut Pasteur, 75724 Paris Cedex 15, France.
Sladek
Frances M
FM
Weiss
Mary C
MC
D016475:3T3 Cells; D000595:Amino Acid Sequence; D000818:Animals; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D050881:E1A-Associated p300 Protein; D018507:Gene Expression Regulation, Developmental; D017930:Genes, Reporter; D051557:Hepatocyte Nuclear Factor 4; D006655:Histone Deacetylases / Q000378:metabolism*; D046911:Macromolecular Substances; D051379:Mice; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D056985:Nuclear Receptor Co-Repressor 2; D051958:Nuclear Receptor Coactivator 2; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D020798:Two-Hybrid System Techniques
D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D004268:DNA-Binding Proteins; D051557:Hepatocyte Nuclear Factor 4; D046911:Macromolecular Substances; C498002:Ncoa2 protein, mouse; C498003:Ncoa2 protein, rat; C539131:Ncor2 protein, mouse; C539132:Ncor2 protein, rat; D009687:Nuclear Proteins; D056985:Nuclear Receptor Co-Repressor 2; D051958:Nuclear Receptor Coactivator 2; D010750:Phosphoproteins; D020033:Protein Isoforms; D018160:Receptors, Cytoplasmic and Nuclear; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; C501970:Tcfl4 protein, mouse; D015534:Trans-Activators; D014157:Transcription Factors; D050881:E1A-Associated p300 Protein; C494361:Ep300 protein, mouse; C494362:Ep300 protein, rat; D006655:Histone Deacetylases