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.
Voleti
Bhavya
B
Department of Pharmacology, James H. Quillen College of Medicine, East Tennessee State University, Johnson City, TN 37614, USA.
Agrawal
Alok
A
D002097:C-Reactive Protein / Q000235:genetics*; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000502:physiology; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000502:physiology*; D005786:Gene Expression Regulation; D006801:Humans; D007375:Interleukin-1 / Q000494:pharmacology; D015850:Interleukin-6 / Q000494:pharmacology; D016328:NF-kappa B / Q000502:physiology*; D050811:Octamer Transcription Factor-1; D011401:Promoter Regions, Genetic; D014157:Transcription Factors / Q000502:physiology*
D022782:CCAAT-Enhancer-Binding Protein-beta; D004268:DNA-Binding Proteins; D007375:Interleukin-1; D015850:Interleukin-6; D016328:NF-kappa B; D050811:Octamer Transcription Factor-1; C494165:POU2F1 protein, human; D014157:Transcription Factors; D002097:C-Reactive Protein