Regulation of Human C-Reactive Protein Gene Expression by Two Synergistic IL-6 Responsive Elements

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Abstract
To study the mechanism of interleukin-6 (IL-6) induction of human C-reactive protein (CRP) gene expression, we have utilized a human hepatoma (PLC/PRF/5) cell culture system to analyze the trans-acting factors which bind to the 300 bp 5‘-flanking region of human CRP gene. In vitro gel mobility shift analyses and methylation interference assays demonstrated that NFIL-6α interacted with two IL-6 responsive elements, and HNF-1α and HNF-3/Octamer-like factors interacted with the downstream IL-6 responsive element in the human CRP promoter. In vivo functional analysis by transient transfection of plasmid constructs containing site-specific mutations in one or two IL-6 responsive elements in the CRP promoter fused to a reporter gene, chloramphenicol acetyl transferase (CAT), demonstrated that the binding of NFIL-6α to two IL-6 responsive elements resulted in synergistic induction of the gene. When HNF-1α or HNF-3/Octamer-like factors were independently bound to their corresponding sites, they had either a positive or negative effect, respectively, on IL-6 inducible transcriptional activity.