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.

PITX2 Isoform-specific Regulation of Atrial Natriuretic Factor Expression

“…Tin has been shown to be both an activator and a repressor of transcription (48,51,52). However, Nkx2.5 has not been shown to act as a repressor, which may be because of the differences in the N-terminal residues between Tin and Nkx2.5 (48).…”

MEF2C is activated by multiple mechanisms in a subset of T-acute lymphoblastic leukemia cell lines

“…Recent data on the NKX2-5 orthologue tinman indicate it functions as a transcriptional activator or repressor, depending on the occurrence of interactions with co-activator or corepressor, respectively. 40 However, CRIPTO is reportedly overexpressed in certain tumor types, 41 rendering a less plausible target for downregulation by NKX2-5. Both PITX2 and MEF2C are involved in hematopoiesis, 42,43 qualifying both of these as potential leukemogenic factors.…”

Mapping activation and repression domains of the vnd/NK-2 homeodomain protein

“…The DNA binding domain is involved in site-specific DNA recognition, and the activation or repression domains interact directly with components of the general transcription machinery (18)(19)(20). There are at least three types of activation domains: acidic (21,22), glutamine-rich (23,24), and proline-rich (25).…”

“…The short tinman domain is located in the N-terminal region of most NK-2-class proteins. The tinman domains of engrailed (32) and NK-4 (20) have been shown to mediate repression. The NK-2-specific domain is located in the C-terminal part of vnd͞NK-2 HD protein and is separated from the HD by a short linker.…”