ROLE OF STAT3 AND C/EBP IN CYTOKINE-DEPENDENT EXPRESSION OF THE MOUSE SERUM AMYLOID P-COMPONENT (SAP) AND C-REACTIVE PROTEIN (CRP) GENES

Abstract

Inflammation is accompanied by a rapid increase in blood levels of acute phase proteins synthesized by hepatocytes in response to cytokines. Although C-reactive protein (CRP) levels increase dramatically in most mammals, the major acute phase protein in the mouse is the homologous pentraxin, serum amyloid P-component (SAP), whereas CRP is a minor acute phase reactant. The molecular basis for the pronounced difference in SAP and CRP gene expression in the mouse is unknown. Transfection of ++/Li mouse hepatoma cells with CAT-reporter constructs containing the 5′-flanking region of the mouse CRP gene indicated that transcription was stimulated by either IL-6, or IL-6 plus IL-1, when ≥360bp of the 5′-proximal DNA was present. Examination of the 5′-flanking region of the mouse SAP gene revealed that the region between −433 and −397 from the transcription start site responded to IL-1 and IL-6 by binding both STAT3 and C/EBPβ. This responsive region consisted of two adjacent C/EBPβ consensus sites that overlap with two STAT3 consensus sites and was found to bind C/EBPβ at an upstream site of −427 to −409 and STAT3 at a downstream site of −415 to −397. By contrast, the 360bp promoter of the CRP gene was bound only by STAT3 at consensus sites at −93, −142, −173, and −287 from the start site; however, a single consensus site for C/EBP at −75 was not recognized. STAT3 appears to be necessary for both mouse SAP and CRP gene transcription since overexpression of an inactive, deletion mutant of STAT3 inhibited transcription of both genes. The results indicate that both STAT3 and C/EBPβ participate in mouse SAP gene expression, whereas only STAT3 is involved in mouse CRP gene expression. The findings for mouse SAP gene expression are consistent with the reported interaction between these two transcription factors for human CRP gene transcription.