OCT-1 acts as a repressor of C-reactive protein gene expression (172.13)

Abstract

Abstract C-reactive protein (CRP), an ancient host-defense plasma protein, is produced by hepatocytes. In Hep3B cells, CRP expression is induced by IL-6; IL-1β synergistically enhances the IL-6 effect. A critical regulatory segment on the CRP promoter contains binding sites for transcription factors C/EBPβ (-48 to -57) and NF-κB (-63 to -74). The κB site overlaps an octamer motif (-59 to -66) which is the binding site for the constitutively expressed transcription factor OCT-1. OCT-1 is known to function both as a transcriptional repressor and activator depending upon the promoter context. The aim of this study was to investigate the function of OCT-1 on the CRP promoter. In luciferase transactivation assays, overexpressed OCT-1 inhibited cytokine-induced CRP expression. EMSA, mutational analysis of the κB site, and the OCT-1 dose-response assays suggested that OCT-1 and NF-κB compete for binding to their overlapping cognate sites. Deletion of the OCT-1 site drastically reduced the cytokine response because the κB site was altered as a consequence of deleting the OCT-1 site. Surprisingly, overexpressed OCT-1 inhibited the residual cytokine-induced CRP expression through the promoter lacking the OCT-1 site. OCT-1 also inhibited overexpressed C/EBPβ-induced CRP expression. We conclude that OCT-1 acts as a repressor of CRP gene expression and it does so by occupying its cognate site on the promoter and also via other transcription factors by an as yet undefined mechanism.