C/EBPα Regulates Hepatic Transcription of Hepcidin, an Antimicrobial Peptide and Regulator of Iron Metabolism

Abstract

Originally identified as a gene up-regulated by iron overload in mouse liver, the HEPC gene encodes hepcidin, the first mammalian liver-specific antimicrobial peptide and potential key regulator of iron metabolism. Here we demonstrate that during rat liver development, amounts of HEPC transcripts were very low in fetal liver, strongly and transiently increased shortly after birth, and reappeared in adult liver. To gain insight into mechanisms that regulate hepatic expression of hepcidin, 5′-flanking regions of human and mouse HEPC genes were isolated and analyzed by functional and DNA binding assays. Human and mouseHEPC promoter-luciferase reporter vectors exhibited strong basal activity in hepatoma HuH-7 and mouse hepatocytes, respectively, but not in non-hepatic U-2OS cells. We found that CCAAT/enhancer-binding protein α (C/EBPα) and C/EBPβ were respectively very potent and weak activators of both human and mouse promoters. In contrast, co-expression of hepatocyte nuclear factor 4α (HNF4α) failed to induce HEPC promoter activity. By electrophoretic mobility shift assay we demonstrated that one putative C/EBP element found in the human HEPCpromoter (−250/−230) predominantly bound C/EBPα from rat liver nuclear extracts. Hepatic deletion of the C/EBPα gene resulted in reduced expression of HEPC transcripts in mouse liver. In contrast, amounts of HEPC transcripts increased in liver-specific HNF4α-null mice. Decrease of hepcidin mRNA in mice lacking hepatic C/EBPα was accompanied by iron accumulation in periportal hepatocytes. Finally, iron overload led to a significant increase of C/EBPα protein and HEPC transcripts in mouse liver. Taken together, these data demonstrate that C/EBPα is likely to be a key regulator of HEPC gene transcription and provide a novel mechanism for cross-talk between the C/EBP pathway and iron metabolism.