Human mutation D157G in ferroportin leads to hepcidin-independent binding of Jak2 and ferroportin down-regulation

Mutations in the iron exporter ferroportin (Fpn) result in iron overload in macrophages or hepatocytes depending upon the mutation. Patients with Fpn mutation D157G show high serum ferritin and normal to slightly elevated transferrin saturation. Here, we show that Fpn(D157G)–green fluorescent protein (GFP) is down-regulated independent of hepcidin, and that this down-regulation is due to the constitutive binding of Jak2 and Fpn phosphorylation. Expression of Fpn(D157G)-GFP in Danio rerio results in a severe growth defect, which can be rescued by iron supplementation. These results identify a hepcidin-independent regulation of Fpn that can result in alterations in iron homeostasis.