Interleukin-6
positive regulation of transcription by RNA polymerase II
STAT3 mediates hepatic hepcidin expression and its inflammatory stimulation.
Hepcidin is a key iron-regulatory hormone produced by the liver. Inappropriately low hepcidin levels cause iron overload, while increased hepcidin expression plays an important role in the anemia of inflammation (AI) by restricting intestinal iron absorption and macrophage iron release. Its expression is modulated in response to body iron stores, hypoxia, and inflammatory and infectious stimuli involving at least in part cytokines secreted by macrophages. In this study we established and characterized IL6-mediated hepcidin activation in the human liver cell line Huh7. We show that the proximal 165 bp of the hepcidin promoter is critical for hepcidin activation in response to exogenously administered IL6 or to conditioned medium from the monocyte/macrophage cell line THP-1. Importantly, we show that hepcidin activation by these stimuli requires a STAT3 binding motif located at position -64/-72 of the promoter. The same STAT binding site is also required for high basal-level hepcidin mRNA expression under control culture conditions, and siRNA-mediated RNA knockdown of STAT3 strongly reduces hepcidin mRNA expression. These results identify a missing link in the acute-phase activation of hepcidin and establish STAT3 as a key effector of baseline hepcidin expression and during inflammatory conditions.