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 mouse HEPC promoterluciferase 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 ␣ (C/EBP␣) and C/EBP␤ were respectively very potent and weak activators of both human and mouse promoters. In contrast, co-expression of hepatocyte nuclear factor 4␣ (HNF4␣) failed to induce HEPC promoter activity. By electrophoretic mobility shift assay we demonstrated that one putative C/EBP element found in the human HEPC promoter (؊250/؊230) predominantly bound C/EBP␣ from rat liver nuclear extracts. Hepatic deletion of the C/EBP␣ gene resulted in reduced expression of HEPC transcripts in mouse liver. In contrast, amounts of HEPC transcripts increased in liver-specific HNF4␣-null mice. Decrease of hepcidin mRNA in mice lacking hepatic C/EBP␣ was accompanied by iron accumulation in periportal hepatocytes. Finally, iron overload led to a significant increase of C/EBP␣ protein and HEPC transcripts in mouse liver. Taken together, these data demonstrate that C/EBP␣ 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.

Estrogen regulates iron homeostasis through governing hepatic hepcidin expression via an estrogen response element

“…CCAAT/enhancer binding protein (C/EBP) was demonstrated to bind this upstream region (Fig. 3B), and C/EBP could activate hepcidin expression in hepatocytes (Courselaud et al, 2002). This finding is supported by a recent study, which demonstrated that the transcription of hepcidin was suppressed by E2 treatment in hepatocytes, HuH7 and HepG2 cells, and this down-regulation could be blocked by the treatment of the E2 antagonist ICI 182780 (Yang et al, 2012).…”

Hemochromatosis

“…Hepcidin deficiency has been associated with the loss of hepcidin itself, HJV, HFE, or TfR2 in humans 3,[7][8][9] and with the inactivation of CCAAT/enhancer binding protein ␣ and mothers against decapentaplegic homolog 4 (Smad4) in mice. 10,11 As for the contribution of nongenetic factors, ethanol abuse (long associated with iron overload) is now believed to inhibit hepcidin transcription. 12,13 Similar effects can be produced by toxic and viral insults (for example, the hepatitis C virus may inhibit hepcidin expression 14 ).…”

The molecular basis of ferroportin-linked hemochromatosis

“…Hepcidin expression is probably transcriptionally regulated (3,4), although the exact mechanisms are not completely defined. The circulating peptide acts as the master regulator of cellular iron export by controlling the concentration of ferroportin (Fpn), an iron exporter present on the basolateral surface of intestinal enterocytes and placental cells and on macrophages and hepatocytes (5)(6)(7).…”