Nucleic Acids Research, 2001, Vol. 29, No. 2 362-372
© 2001 Oxford University Press
Analysis of the Xenopus laevis CCAAT-enhancer binding protein 
gene promoter demonstrates species-specific differences in the mechanisms for both auto-activation and regulation by Sp1
Cardiff School of Biosciences, Cardiff University, Museum Avenue, PO Box 911, Cardiff CF10 3US, UK
Transcription factors belonging to the CCAAT-enhancer binding protein (C/EBP) family have been implicated in the regulation of gene expression during differentiation, development and disease. Autoregulation is relatively common in the modulation of C/EBP gene expression and the murine and human C/EBP
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 genes from a wider range of different species be investigated in order to gauge the degree of commonality, or otherwise, that may exist. We report here studies that investigate the regulation of the Xenopus laevis C/EBP gene (xC/EBP). The –1131/+41 promoter region was capable of directing high levels of expression in both the human hepatoma Hep3B and the Xenopus kidney epithelial A6 cell lines, and was auto-activated by expression vectors specifying for xC/EBP or xC/EBPß. Deletion analysis showed that the –321/+41 sequence was sufficient for both the constitutive promoter activity and auto-activation and electrophoretic mobility shift assays identified the interaction of C/EBPs and Sp1 to this region. Although deletion of either the C/EBP or the Sp1 site drastically reduced the xC/EBP promoter activity, multimers of only the C/EBP site could confer autoregulation 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 promoter was subject to direct autoregulation. In addition, we demonstrate a novel species-specific action of Sp1 in the regulation of C/EBP expression, with the factor able to repress the murine promoter but activate the Xenopus gene.
* To whom correspondence should be addressed. Tel: +44 292 0876753; Fax: +44 292 0874116; Email: ramji{at}cardiff.ac.uk Present addresses: Feray Tura Kockar, Molecular Biology Section, Department of Biology, University of Balikesir, Balikesir, Turkey Stavroula Kousteni, University of Arkansas for Medical Sciences, Division of Endocrinology and Metabolism, Department of Internal Medicine and Center for Osteoporosis, Slot 587, 4301 West Markham Street, Little Rock, AR 72205-7199, USA
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