Identification of Multiple Protein Binding Domains in the Promoter-regulatory Region of the Phosphoenolpyruvate Carboxykinase (GTP) Gene

Transcription of the gene for the cytosolic form of phosphoenolpyruvate carboxykinase (GTP) (EC 4.1.1.32) (PEPCK) from the rat is acutely regulated by a number of hormones, including glucagon (acting via cAMP), glucocorticoids, and insulin. In this study we demonstrate by DNase I footprinting that a region of the PEPCK promoter, extending from -460 to +73, contained eight protein binding domains. Two nuclear proteins protected adjacent sites from -121 to -99 and -96 to -77, which have been previously shown to be involved in maintaining the level of basal gene transcription and conferring cAMP responsiveness, respectively. Oligonucleotide competition studies suggested that the protein(s) binding to the cAMP-responsive element (CRE) occupies a second site at -147 to -130, which has a high degree of sequence homology to the CRE, and also binds to two other elements that show partial sequence homologies. The protein(s) which bound to these four elements copurified through oligonucleotide affinity chromatography, suggesting that the PEPCK promoter has four binding sites for the CRE-binding protein(s). Potential tissue-specific elements in the PEPCK promoter were identified by footprinting with nuclear extracts prepared from rat liver, kidney, brain, and spleen. The multiple protein-binding sites in this promoter-regulatory region reflect the complex transcriptional regulation that is characteristic of this gene.