The protein EP300 and its paralog CREBBP (CREB-binding protein) are ubiquitously expressed transcriptional co-activators and histone acetyl transferases. The gene EP300 is essential for normal cardiac and neural development, whereas CREBBP is essential for neurulation, hematopoietic differentiation, angiogenesis and skeletal and cardiac development. Mutations in CREBBP cause Rubinstein-Taybi syndrome, which is characterized by mental retardation, skeletal abnormalities and congenital cardiac defects. The CBP/p300-interacting transactivator with ED-rich tail 2 (CITED2) binds EP300 and CREBBP with high affinity and regulates gene transcription. Here we show that Cited2-/- embryos die with cardiac malformations, adrenal agenesis, abnormal cranial ganglia and exencephaly. The cardiac defects include atrial and ventricular septal defects, overriding aorta, double-outlet right ventricle, persistent truncus arteriosus and right-sided aortic arches. We find increased apoptosis in the midbrain region and a marked reduction in ErbB3-expressing neural crest cells in mid-embryogenesis. We show that CITED2 interacts with and co-activates all isoforms of transcription factor AP-2 (TFAP2). Transactivation by TFAP2 isoforms is defective in Cited2-/- embryonic fibroblasts and is rescued by ectopically expressed CITED2. As certain Tfap2 isoforms are essential in neural crest, neural tube and cardiac development, we propose that abnormal embryogenesis in mice lacking Cited2 results, at least in part, from its role as a Tfap2 co-activator.
Members of the CREB-binding protein/p300-interacting transactivator with ED-rich tail (CITED) family bind CREB-binding protein and p300 with high affinity and regulate gene transcription. Gene knockout studies indicate that CITED2 is required for neural crest and neural tube development and that it functions as a co-activator for transcription factor AP-2 (TFAP2). Here we describe human CITED4, a new member of this family, which is encoded by a single exon mapping to chromosome 1p34 -1p35. CITED4 and p300/CREB-binding protein are present in endogenous naturally occurring complexes, indicating that they interact physiologically. The interaction occurs between the cysteine-histidinerich domain 1 of p300 and the carboxyl terminus of CITED4. In keeping with this, CITED4 functions as a transactivator when artificially targeted to a promoter element. CITED4 physically interacts with all TFAP2 isoforms in vitro and strongly co-activates all TFAP2 isoforms in Hep3B cells. Co-activation of TFAP2 requires amino-terminal and carboxyl-terminal residues of CITED4. In HepG2 cells, CITED4 is significantly weaker than CITED2 for TFAP2C co-activation. These results suggest that CITED4 may function as a co-activator for TFAP2. They also suggest the existence of cell type-and TFAP2 isoform-specific co-activation by CITED2 and CITED4, which may result in differential modulation of TFAP2 function.
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