Hepcidin is encoded as an 84 amino acid prepropeptide containing a typical 
N-terminal 24 amino acid endoplasmic reticulum targeting signal sequence, and a 
35 amino acid proregion (pro) with a consensus furin cleavage site immediately 
followed by the C-terminal 25 amino acid bioactive iron-regulatory hormone 
(mature peptide). We performed pulse-chase studies of posttranslational 
processing of hepcidin in human hepatoma HepG2 cells and in primary human 
hepatocytes induced with bone morphogenic protein (BMP-9). In some experiments, 
the cells were treated with the furin protease inhibitor 
decanoyl-Arg-Val-Lys-Arg-chloromethylketone (CMK) or furin siRNA. In the absence 
of furin inhibitor, hepcidin was found to be processed in less than 1 h and 
secreted as a 3 kDa form reactive with anti-mature but not anti-pro antibody. In 
the presence of furin inhibitors or furin siRNA, a 6 kDa form reactive with both 
anti-pro and anti-mature antibody was rapidly secreted into the medium. 
Processing was not affected by inhibitors of the hypoxia inducible factor (HIF) 
pathway, or by treatment with 30 microM holo- or apo-transferrin. In conclusion, 
the hepatic prohormone convertase furin mediates the posttranslational 
processing of hepcidin. The proteolytic cleavage of prohepcidin to hepcidin is 
not regulated by iron-transferrin or the HIF pathway.