Analysis of the Xenopus laevis CCAAT-enhancer binding protein alpha gene promoter demonstrates species-specific differences in the mechanisms for both auto-activation and regulation by Sp1

Transcription factors belonging to the CCAAT-enhancer binding protein (C/EB P) family have been implicated in the regulation of gene expression during differentiation, development and disease. Autoregulation is relatively comm on in the modulation of C/EBP gene expression and the murine and human C/EB P alpha genes have been shown to be auto-activated by different mechanisms. In the light of this finding, it is essential that autoregulation of C/EBP alpha genes from a wider range of different species be investigated in ord er to gauge the degree of commonality, or otherwise, that may exist. We rep ort here studies that investigate the regulation of the Xenopus laevis C/EB P alpha gene (xC/EBP alpha), The -1131/+41 promoter region was capable of d irecting high levels of expression in both the human hepatoma Hep3B and the Xenopus kidney epithelial As cell lines, and was auto-activated by express ion vectors specifying for xC/EBP alpha or xC/EBP beta. Deletion analysis s howed that the -321/+41 sequence was sufficient for both the constitutive p romoter activity and auto-activation and electrophoretic mobility shift ass ays identified the interaction of C/EBPs and Sp1 to this region. Although d eletion of either the C/EBP or the Sp1 site drastically reduced the xC/EBP alpha promoter activity, multimers of only the C/EBP site could confer auto regulation to a heterologous SV40 promoter. These results indicate that, in contrast to the human promoter and in common with the murine gene, the xC/ EBP alpha promoter was subject to direct autoregulation, In addition, we de monstrate a novel species-specific action of Sp1 in the regulation of C/EBP alpha expression, with the factor able to repress the murine promoter but activate the Xenopus gene.