Analysis of the promoter element of the serum amyloid A gene and its interaction with constitutive and inducible nuclear factors from rabbit liver.

In an effort to identify regulatory elements of the serum amyloid A (SAA) gene that play a major role in its expression under acute-phase conditions, we studied the expression of a set of chimeric SAA-chloramphenicol acetyltransferase (CAT) plasmids containing a progressively deleted upstream 5' sequence of the SAA gene. Two regulatory regions (-314 to -135 and -135 to -31) capable of driving cytokine-induced transcription have been identified. Gel retardation assays revealed that the regulatory region located between positions -314 and -135 is a major site of interaction for highly inducible and constitutive nuclear proteins in acute-phase rabbit liver. DNase I footprint and competition analyses showed that this region contains two adjacent nuclear protein binding sites (between -191 and -140) with varying affinity for protein binding. Both of these binding sites are capable of driving cytokine-induced transcription of a reporter gene containing a minimal promoter. Detailed analyses of the inducible nuclear proteins that bind to this promoter element showed that they are homologues of the CCAAT/enhancer binding protein (C/EBP) family. Accumulation of the inducible nuclear factors under acute conditions, when maximal transcription activity has been reported, suggests a critical role for these proteins in the expression of the SAA gene.