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B on the Proximal Promoter
Department of Pharmacology, James H. Quillen College of Medicine, East Tennessee State University, Johnson City, TN 37614
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/EBP
. 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-
B, a transcription factor activated by IL-1 in Hep3B cells, has been shown to increase endogenous CRP expression. The purpose of this study was to investigate the possible action of NF-B on the 157 bp of the proximal promoter. In this study we show that NF-B requires and acts synergistically with C/EBP on the CRP-proximal promoter to regulate CRP expression. We located the regulatory element that consisted of overlapping binding sites for NF-B (p50-p50 and p50-p65) and OCT-1. The B site was responsible for the synergy between NF-B and C/EBP and was also necessary for the CRP transactivation by C/EBP through the C/EBP site. Mutation of the B site decreased the synergistic effect of IL-1 on IL-6-induced CRP expression. Basal CRP expression increased dramatically when binding of both OCT-1 and NF-B 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/EBP. This model for CRP expression favors the variation seen in baseline serum CRP levels in a normal healthy population.
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