Molecular Characterization of the XenopusCCAAT-Enhancer Binding Protein β Gene Promoter

Transcription factors belonging to the CCAAT-enhancer binding protein (C/EBP) family play key roles in the regulation of genes implicated in the control of growth, differentiation, metabolism, and inflammation. The recent limited studies on the promoter regions of C/EBP genes, particularly C/EBPα, have indicated the potential existence of species-specific regulatory mechanisms. It is therefore essential that the promoter regions of different C/EBP genes from a wide range of species are investigated in detail. As an important step toward this goal, we report here the characterization of the Xenopus laevisC/EBPβ gene promoter. Sequence analysis showed that the 1.6-kb promoter region contained putative binding sites for several transcription factors that have previously been implicated in the regulation of the C/EBPs, including C/EBP, CREB, Myb, STAT, and USF. The −288/+91 promoter region was capable of directing high levels of expression in the hepatoma Hep3B cell line. In addition, this minimal promoter could be autoregulated by both C/EBPα and C/EBPβ and activated by lipopolysaccharide, interleukin-6 and CREB. These results therefore demonstrate that several aspects of C/EBPβ regulation in mammals have been highly conserved in amphibians. However, a comparison of C/EBPβ gene promoters characterized to date does indicate the existence of species-specific differences in autoregulation.