Hepcidin and ferroportin: the new players in iron metabolism.

Systemic iron homeostasis is regulated by the interaction of the peptide hormone, hepcidin and the iron exporter, ferroportin. Mutations in FPN1, the gene that encodes ferroportin, result in iron-overload disease that shows dominant inheritance and variation in phenotype. The inheritance of ferroportin-linked disorders can be explained by the finding that ferroportin is a multimer and the product of the mutant allele participates in multimer formation. The nature of the ferroportin mutant can explain the variation in phenotype, which is due to either decreased iron export activity or decreased ability to be downregulated by hepcidin. Iron export through ferroportin is determined by the concentration of ferroportin in plasma membrane, which is the result of both synthetic and degradation events. Ferroportin degradation can occur by hepcidin-dependent and hepcidin-independent internalization. Ferroportin expression is regulated transcriptionally and posttranslationally.