title: Homeodomain and winged-helix transcription factors recruit activated Smads to distinct promoter elements via a common Smad interaction motif.
abstract: We have investigated the regulation of the activin-inducible distal element (DE) of the Xenopus goosecoid promoter. The results show that paired-like homeodomain transcription factors of the Mix family, Mixer and Milk, but not Mix.1, mediate activin/TGF-beta-induced transcription through the DE by interacting with the effector domain of Smad2, thereby recruiting active Smad2/Smad4 complexes to the Mixer/Milk-binding site. We identify a short motif in the carboxyl termini of Mixer and Milk, which is demonstrated to be both necessary and sufficient for interaction with the effector domain of Smad2 and is required for mediating activin/TGF-beta-induced transcription. This motif is not confined to these homeodomain proteins, but is also present in the Smad2-interacting winged-helix proteins Xenopus Fast-1, human Fast-1, and mouse Fast-2. We demonstrate directly that transcription factors of different DNA-binding specificity recruit activated Smads to distinct promoter elements via a common mechanism. These observations, together with the temporal and spatial expression patterns of Mixer and Milk, lead us to propose a model for mesoendoderm formation in Xenopus in which these homeodomain transcription factor/Smad complexes play a role in initiating and maintaining transcription of target genes in response to endogenous activin-like signals.
authors.affiliation: Laboratory of Developmental Signalling, Imperial Cancer Research Fund, WC2A 3PX London, UK.
authors.forename: S
authors.initials: S
authors.lastname: Germain
authors.forename: M
authors.initials: M
authors.lastname: Howell
authors.forename: G M
authors.initials: GM
authors.lastname: Esslemont
authors.forename: C S
authors.initials: CS
authors.lastname: Hill
mesh_terms: D028341:Activins; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D003513:Cycloheximide / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000378:metabolism* / Q000502:physiology; D051858:Forkhead Transcription Factors; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D051956:Goosecoid Protein; D018398:Homeodomain Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics* / Q000502:physiology*; D017874:Immediate-Early Proteins / Q000235:genetics / Q000502:physiology*; D007265:Inhibins / Q000502:physiology; D046911:Macromolecular Substances; D008648:Mesoderm / Q000502:physiology*; D008969:Molecular Sequence Data; D009024:Morphogenesis / Q000235:genetics; D009414:Nerve Growth Factors; D011401:Promoter Regions, Genetic; D017434:Protein Structure, Tertiary; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D012097:Repressor Proteins; D051785:Smad Proteins; D051899:Smad2 Protein; D051901:Smad4 Protein; D015534:Trans-Activators / Q000378:metabolism*; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000502:physiology; D029867:Xenopus Proteins; D014982:Xenopus laevis / Q000196:embryology
chemical_list: C115868:Bix1 protein, Xenopus; D004268:DNA-Binding Proteins; C102067:FOXH1 protein, Xenopus; C510350:FOXH1 protein, human; D051858:Forkhead Transcription Factors; C491117:Foxh1 protein, mouse; D051956:Goosecoid Protein; D018398:Homeodomain Proteins; D017874:Immediate-Early Proteins; D046911:Macromolecular Substances; C100368:Mix1 protein, Xenopus; D009414:Nerve Growth Factors; D011500:Protein Synthesis Inhibitors; D012097:Repressor Proteins; D051785:Smad Proteins; D051899:Smad2 Protein; C497785:Smad2 protein, Xenopus; D051901:Smad4 Protein; C490810:Smad4 protein, mouse; D015534:Trans-Activators; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D029867:Xenopus Proteins; C405705:mixer protein, Xenopus; C490808:smad4.1 protein, Xenopus; C117263:smad4.2 protein, Xenopus; D028341:Activins; D007265:Inhibins; D003513:Cycloheximide