CCAAT/enhancer-binding protein activates the CD14 promoter and mediates transforming growth factor β 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 CfEBPα and CfEBPβ during U937 monocytic cell differentiation, and we found CfEBPα and CfEBPβ 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.