| Abstract
| - The promoter region of the mouse CCAAT-Enhancer Binding Protein (C/EBPα) gene Is capable of directing high levels of expression of reporter constructs In various cell lines, albeit even In cells that do not express their endogenous C/EBPα gene. To understand the molecular mechanisms underlying this ubiquitous expression, we have characterized the promoter region of the mouse C/EBPα gene by a variety of in vitro and in vivo methods. We show that three sites related in sequence to USF, BTE and C/EBP binding sites and present In promoter region −350/+ 3, are recognized by proteins from rat liver nuclear extracts. The sequence of the C/EBPα promoter that Includes the USF binding site Is also capable of forming stable complexes with purified Myc + Max heterodlmers and mutation of this site drastically reduces transcription of C/EBPα promoter luclferase constructs both in liver and non liver cell lines. In addition, we Identify three novel protein-binding sites two of which display similarity to NF-1 and a NFxB binding sites. The region located between nucleotides −197 and −178 forms several heat-stable complexes with liver nuclear proteins in vitro which are recognized mainly by antibodies specific for C/EBPα. Furthermore, transient expression of C/EBPα and to a lesser extent C/EBPβ expression vectors, results in transactlvatlon of a co-transfected C/EBPα promoter-luclferase reporter construct. These experiments support the notion that the C/EBPα gene Is regulated by C/EBPα but other C/EBP-related proteins may also be Involved.
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