CCAAT/ENHANCER-BINDING PROTEIN ACTIVATES THE CD14 PROMOTER AND MEDIATES TRANSFORMING GROWTH FACTOR BETA SIGNALING IN MONOCYTE DEVELOPMENT

Abstract Transcription factors from the CCAAT/enhancer-binding protein (C/EBP) family play important roles in myeloid cell differentiation. CD14 is a monocyte/macrophage differentiation marker and is strongly up-regulated during monocytic cell differentiation. Here, we report the direct binding of C/EBP to the monocyte-specific promoter of CD14. Transactivation analyses demonstrate that C/EBP family members significantly activate the CD14 promoter. These data indicate that C/EBP is directly involved in the regulation of CD14 gene expression. When myelomonoblastic U937 cells are treated with vitamin D3 and TGF-β, they differentiate toward monocytic cells. Using specific antibodies against different C/EBP family members in electrophoretic mobility shift assays and Western blot assays, we have identified a specific increase in the DNA binding and the expression of C/EBPα and C/EBPβ during U937 monocytic cell differentiation, and we found C/EBPα and C/EBPβ bind to the promoter in heterodimer. Furthermore, with stably transfected cell lines, we demonstrate that the C/EBP binding site in the CD14 promoter plays a critical role for mediating TGF-β signaling in the synergistic activation of CD14 expression by vitamin D3 and TGF-β during U937 differentiation. This may indicate that C/EBPs have important functions in the process of TGF-β signal transduction during monocyte differentiation.