RESUMO
GATA4 is a transcriptional activator of cardiac-restricted promoters and is required for normal cardiac morphogenesis. Friend of GATA-2 (FOG-2) is a multizinc finger protein that associates with GATA4 and represses GATA4-dependent transcription. To better understand the transcriptional repressor activity of FOG-2 we performed a functional analysis of the FOG-2 protein. The results demonstrated that 1) zinc fingers 1 and 6 of FOG-2 are each capable of interacting with evolutionarily conserved motifs within the N-terminal zinc finger of mammalian GATA proteins, 2) a nuclear localization signal (RKRRK) (amino acids 736-740) is required to program nuclear targeting of FOG-2, and 3) FOG-2 can interact with the transcriptional co-repressor, C-terminal-binding protein-2 via a conserved sequence motif in FOG-2 (PIDLS). Surprisingly, however, this interaction with C-terminal-binding protein-2 is not required for FOG-2-mediated repression of GATA4-dependent transcription. Instead, we have identified a novel N-terminal domain of FOG-2 (amino acids 1-247) that is both necessary and sufficient to repress GATA4-dependent transcription. This N-terminal repressor domain is functionally conserved in the related protein, Friend of GATA1. Taken together, these results define a set of evolutionarily conserved mechanisms by which FOG proteins repress GATA-dependent transcription and thereby form the foundation for genetic studies designed to elucidate the role of FOG-2 in cardiac development.
Assuntos
Proteínas de Transporte/metabolismo , Proteínas de Ligação a DNA/metabolismo , Proteínas de Membrana Transportadoras , Proteínas Repressoras/metabolismo , Fatores de Transcrição , Células 3T3 , Oxirredutases do Álcool , Sequência de Aminoácidos , Animais , Sítios de Ligação , Proteínas de Transporte/genética , Proteínas de Ligação a DNA/química , Proteínas de Ligação a DNA/genética , Imunofluorescência , Proteínas da Membrana Plasmática de Transporte de GABA , Regulação da Expressão Gênica , Camundongos , Dados de Sequência Molecular , Mutagênese , Sinais de Localização Nuclear , Fosfoproteínas/metabolismo , Ligação Proteica , Proteínas Repressoras/genética , Homologia de Sequência de Aminoácidos , Transfecção , Dedos de Zinco/genéticaRESUMO
GATA transcription factors are important regulators of both hematopoiesis (GATA-1/2/3) and cardiogenesis (GATA-4) in mammals. The transcriptional activities of the GATA proteins are modulated by their interactions with other transcription factors and with transcriptional coactivators and repressors. Recently, two related zinc finger proteins, U-shaped (USH) and Friend of GATA-1 (FOG) have been reported to interact with the GATA proteins Pannier and GATA-1, respectively, and to modulate their transcriptional activities in vitro and in vivo. In this report, we describe the molecular cloning and characterization of a third FOG-related protein, FOG-2. FOG-2 is an 1,151 amino acid nuclear protein that contains eight zinc finger motifs that are structurally related to those of both FOG and USH. FOG-2 is first expressed in the mouse embryonic heart and septum transversum at embryonic day 8.5 and is subsequently expressed in the developing neuroepithelium and urogenital ridge. In the adult, FOG-2 is expressed predominately in the heart, brain, and testis. FOG-2 associates physically with the N-terminal zinc finger of GATA-4 both in vitro and in vivo. This interaction appears to modulate specifically the transcriptional activity of GATA-4 because overexpression of FOG-2 in both NIH 3T3 cells and primary rat cardiomyocytes represses GATA-4-dependent transcription from multiple cardiac-restricted promoters. Taken together, these results implicate FOG-2 as a novel modulator of GATA-4 function during cardiac development and suggest a paradigm in which tissue-specific interactions between different FOG and GATA proteins regulate the differentiation of distinct mesodermal cell lineages.
