Regulation of basal and induced expression of C-reactive protein through an overlapping element for OCT-1 and NF-kappaB on the proximal promoter.

C-reactive protein (CRP) is an acute phase protein produced by hepatocytes. A minor elevation in the baseline levels of serum CRP is considered an indicator of chronic inflammation. In hepatoma Hep3B cells, IL-6 induces CRP expression by activating transcription factors STAT3 and C/EBPbeta. IL-1 synergistically enhances the effects of IL-6. The first 157 bp of the CRP promoter are sufficient for IL-1 synergy. Previously, NF-kappaB, a transcription factor activated by IL-1beta in Hep3B cells, has been shown to increase endogenous CRP expression. The purpose of this study was to investigate the possible action of NF-kappaB on the 157 bp of the proximal promoter. In this study we show that NF-kappaB requires and acts synergistically with C/EBPbeta on the CRP-proximal promoter to regulate CRP expression. We located the regulatory element that consisted of overlapping binding sites for NF-kappaB (p50-p50 and p50-p65) and OCT-1. The kappaB site was responsible for the synergy between NF-kappaB and C/EBPbeta and was also necessary for the CRP transactivation by C/EBPbeta through the C/EBP site. Mutation of the kappaB site decreased the synergistic effect of IL-1beta on IL-6-induced CRP expression. Basal CRP expression increased dramatically when binding of both OCT-1 and NF-kappaB was abolished. Combined data from luciferase transactivation assays and EMSA lead us to conclude that the binding of OCT-1 to the promoter, facilitated by p50-p50 in a novel way, represses, whereas replacement of OCT-1 by p50-p65 induces CRP transcription in cooperation with C/EBPbeta. This model for CRP expression favors the variation seen in baseline serum CRP levels in a normal healthy population.