β-catenin binds to the downstream region and regulates the expression C-reactive protein gene

C-Reactive protein (CRP) is a major acute-phase response protein, which is activated by various cytokines. We investigated the mechanism of TNF-alpha-induced CRP expression and found that the p50 subunit of NF-kappa B was responsible for the transcriptional activation of CRP. Since the p50 protein acts as a positive regulator of CRP expression without an inherent transactivation domain, we looked for an interaction partner that could provide p50 with such a domain. We found that beta-catenin enhanced the expression of a CRP mRNA in concert with p50 subunit. Protein - protein interaction between p50 and beta-catenin was important for CRP expression and their interactions to CRP promoter were induced after TNF-alpha treatment. Since gene expression depends upon the proximity of promoters and distal regulatory sites, we explored the long-range genomic interaction at the CRP locus by chromosome conformation capture (3C). We identified a binding site for beta-catenin in the downstream of CRP gene by 3C and confirmed TNF-alpha-induced association of beta-catenin and p50 by chromatin immunoprecipitation and co-immunoprecipitation assays. Our findings provide evidence that transcription of the CRP gene depends upon p50 and beta-catenin proteins, which is accompanied by close proximity between promoter and the downstream region of CRP gene.