Evidence for the involvement of at least two distinct transcription factors, one of which is liver-enriched, for the activation of the phosphoenolpyruvate carboxykinase gene promoter by cAMP.

A detailed analysis of the promoter sequence requirements for the cAMP induction of transcription of the gene for phosphoenolpyruvate carboxykinase (GTP) (EC 4.1.1.32) was undertaken. It was determined that the cAMP-responsive unit of this promoter consisted of two independently weak or inactive components; the typical cAMP response element (CRE) sequence located at position -85 and a region of the promoter extending from -300 to -230 which contained multiple binding sites for liver-enriched nuclear proteins. A previous study had indicated that multiple binding sites are critical for the activity of this latter region (Liu, J., Park, E. A., Gurney, A. L., Roesler, W. J., and Hanson, R. W. (1991) J. Biol. Chem. 266, 19095-19102). In the present study, we extend this observation by demonstrating that the activity of this region can be effectively substituted for by three copies of just one subsite present in that region. This would suggest that the binding of three molecules of a single liver-enriched factor is what forms this component of the cAMP response unit. The other component of the cAMP response unit, the CRE, has been shown previously to be bound by these same liver-enriched factors as well as by cAMP response element binding protein, leading to some debate as to the identity of the protein mediating the cAMP response through this element. By two different experimental approaches, we show that neither CCAAT/enhancer binding protein nor D-site binding protein is the likely mediator of the cAMP response through the CRE, while cAMP response element binding protein is a possible candidate.