title: The homeodomain transcription factor NK-4 acts as either a transcriptional activator or repressor and interacts with the p300 coactivator and the Groucho corepressor.
abstract: NK-4 (tinman) encodes an NK-2 class homeodomain transcription factor that is required for development of the Drosophila dorsal mesoderm, including heart. Genetic evidence suggests its important role in mesoderm subdivision, yet the properties of NK-4 as a transcriptional regulator and the mechanism of gene transcription by NK-4 are not completely understood. Here, we describe its properties as a transcription factor and its interaction with the p300 coactivator and the Groucho corepressor. We demonstrate that NK-4 can activate or repress target genes in cultured cells, depending on functional domains that are conserved between Drosophila melanogaster and Drosophila virilis NK-4 genes. Using GAL4-NK-4 fusion constructs, we have mapped a transcriptional activation domain (amino acids 1-110) and repression domains (amino acids 111-188 and the homeodomain) and found an inhibitory function for the homeodomain in transactivation by NK-4. Furthermore, we demonstrate that NK-4-dependent transactivation is augmented by the p300 coactivator and show that NK-4 physically interacts with p300 via the activation domain. In addition, cotransfection experiments indicate that the repressor activity of NK-4 is strongly enhanced by the Groucho corepressor. Using immunoprecipitation and in vitro pull-down assays, we show that NK-4 directly interacts with the Groucho corepressor, for which the homeodomain is required. Together, our results indicate that NK-4 can act as either a transcriptional activator or repressor and provide the first evidence of NK-4 interactions with the p300 coactivator and the Groucho corepressor.
authors.affiliation: Laboratory of Molecular Cardiology, NHLBI, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: C Y
authors.initials: CY
authors.lastname: Choi
authors.forename: Y M
authors.initials: YM
authors.lastname: Lee
authors.forename: Y H
authors.initials: YH
authors.lastname: Kim
authors.forename: T
authors.initials: T
authors.lastname: Park
authors.forename: B H
authors.initials: BH
authors.lastname: Jeon
authors.forename: R A
authors.initials: RA
authors.lastname: Schulz
authors.forename: Y
authors.initials: Y
authors.lastname: Kim
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins; D001665:Binding Sites; D017124:Conserved Sequence; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004330:Drosophila / Q000235:genetics; D029721:Drosophila Proteins; D005786:Gene Expression Regulation; D009687:Nuclear Proteins / Q000378:metabolism*; D011233:Precipitin Tests; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism*; D017384:Sequence Deletion; D015534:Trans-Activators / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D009687:Nuclear Proteins; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D015534:Trans-Activators; C091023:gro protein, Drosophila; C102933:tin protein, Drosophila