Defective targeting of hemojuvelin to plasma membrane is a common pathogenetic mechanism in juvenile hemochromatosis.

نویسندگان

  • Laura Silvestri
  • Alessia Pagani
  • Claudia Fazi
  • Gianmario Gerardi
  • Sonia Levi
  • Paolo Arosio
  • Clara Camaschella
چکیده

Hemojuvelin (HJV) positively modulates the iron regulator hepcidin, and its mutations are the major cause of juvenile hemochromatosis (JH), a recessive disease leading to iron overload. Defective HJV reduces hepcidin up-regulation both in humans and in Hjv-deficient mice. To investigate the JH pathogenesis and the functional properties of human HJV we studied the biosynthesis and maturation of 6 HJV pathogenic mutants in HeLa and HepG2 cells. We show that proteolytic processing is defective in mutants F170S, W191C, and G320V, but not in G99V and C119F. Moreover, we show that mutants G99V and C119F are targeted to the cell surface, while F170S, W191C, G320V, and R326X (lacking the glycosilphosphatidylinositol [GPI] anchor) are mainly retained in the endoplasmic reticulum, although all mutants are released as soluble forms (s-HJV) in a proportion that is modulated by iron supplementation. Membrane HJV (m-HJV) is mainly composed of the cleaved protein, and its level is increased by iron in wild-type (WT) mice but not in the mutants. Altogether, the data demonstrate that the loss of HJV membrane export is central to the pathogenesis of JH, and that HJV cleavage is essential for the export. The results support a dual function for s- and m-HJV in iron deficiency and overload, respectively.

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منابع مشابه

RED CELLS Defective targeting of hemojuvelin to plasma membrane is a common pathogenetic mechanism in juvenile hemochromatosis

Hemojuvelin (HJV) positively modulates the iron regulator hepcidin, and its mutations are the major cause of juvenile hemochromatosis (JH), a recessive disease leading to iron overload. Defective HJV reduces hepcidin up-regulation both in humans and in Hjv-deficient mice. To investigate the JH pathogenesis and the functional properties of human HJV we studied the biosynthesis and maturation of ...

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Hemojuvelin N-terminal mutants reach the plasma membrane but do not activate the hepcidin response.

BACKGROUND Hemojuvelin is a glycosylphosphatidylinositol-anchored protein, expressed in liver, skeletal muscle and heart. As a co-receptor of bone morphogenetic protein, membrane hemojuvelin positively modulates the iron regulator hepcidin. Mutations of the gene encoding for hemojuvelin cause juvenile hemochromatosis, characterized by hepcidin deficiency and severe iron overload. We have previo...

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Competitive regulation of hepcidin mRNA by soluble and cell-associated hemojuvelin.

Mutations in a recently identified gene HJV (also called HFE2, or repulsive guidance molecule C, RgmC) are the major cause of juvenile hemochromatosis (JH). The protein product of HJV, hemojuvelin, contains a C-terminal glycosylphosphatidylinositol anchor, suggesting that it can be present in either a soluble or a cell-associated form. Patients with HJV hemochromatosis have low urinary levels o...

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Hemojuvelin (HJV)-associated hemochromatosis: analysis of HJV and HFE mutations and iron overload in three families.

Juvenile hemochromatosis is a severe form of hereditary iron overload. It can be caused by mutations in either hepcidin or hemojuvelin genes. In this study we identified the molecular basis of juvenile hemochromatosis in three Australian families and assessed the role of potential modifying genes in individuals carrying HFE mutations.

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Genetic abnormalities and juvenile hemochromatosis: mutations of the HJV gene encoding hemojuvelin.

Juvenile hemochromatosis is an early-onset form of iron storage disease characterized by hypogonadotrophic hypogonadism and cardiomyopathy. Recently, the putative causative gene (LOC148738) encoding a protein designated hemojuvelin was cloned. The previously proposed designation of this gene as HFE2 is contrary to established convention, because it is not a member of the HFE family. We suggest ...

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عنوان ژورنال:
  • Blood

دوره 109 10  شماره 

صفحات  -

تاریخ انتشار 2007