Abstract
CCAAT/enhancer-binding protein (C/EBP) family members are transcription factors involved in important physiological processes, such as cellular proliferation and differentiation, regulation of energy homeostasis, inflammation, and hematopoiesis. Transcriptional activation by C/EBPα and C/EBPβ involves the coactivators CREB-binding protein (CBP) and p300, which promote transcription by acetylating histones and recruiting basal transcription factors. In this study, we show that C/EBPδ is also using CBP as a coactivator. Based on sequence homology with C/EBPα and -β, we identify in C/EBPδ two conserved amino acid segments that are necessary for the physical interaction with CBP. Using reporter gene assays, we demonstrate that mutation of these residues prevents CBP recruitment and diminishes the transactivating potential of C/EBPδ. In addition, our results indicate that C/EBP family members not only recruit CBP but specifically induce its phosphorylation. We provide evidence that CBP phosphorylation depends on its interaction with C/EBPδ and define point mutations within one of the two conserved amino acid segments of C/EBPδ that abolish CBP phosphorylation as well as transcriptional activation, suggesting that this new mechanism could be important for C/EBP-mediated transcription.