Evidence That Inhibition of Hemojuvelin Shedding in Response to Iron Is Mediated through Neogenin

Zhang, An Sheng; Anderson, Sheila A.; Meyers, Kathrin R.; Hernandez, Catalina; Eisenstein, Richard S.; Enns, Caroline A.

doi:10.1074/jbc.m608788200

Cited by 111 publications

(185 citation statements)

References 41 publications

(74 reference statements)

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“…During a cis interaction between HJV and neogenin on muscle cells, membrane-bound HJV may be required to bend over to access its binding epitope on the membrane-proximal FNIII 5-6 domains, thereby possibly exposing it to cleavage. Thus the mapping of the HJV binding epitope on neogenin to its most membrane-proximal domain may help to explain the correlation between neogenin binding and HJV shedding (28).…”

Section: Discussionmentioning

confidence: 99%

Neogenin Interacts with Hemojuvelin through Its Two Membrane-Proximal Fibronectin Type III Domains

et al. 2008

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Hemojuvelin is a recently identified iron-regulatory protein that plays an important role in affecting the expression of hepcidin, a key iron regulatory hormone. Although the underlying mechanism of this process is not clear, several hemojuvelin-binding proteins, including the cell surface receptor neogenin and bone morphogenetic protein (BMP) cytokines, have been identified. The ectodomain of neogenin is composed of four immunoglobulin-like (Ig) domains followed by six fibronectin type III-like (FNIII) domains. Here we report expression of soluble versions of hemojuvelin and neogenin for biochemical characterization of their interaction and the interaction of HJV with BMP-2. Hemojuvelin normally undergoes an autocatalytic cleavage, and as in ViVo, recombinant hemojuvelin exists as a mixture of cleaved and uncleaved forms. Neogenin binds to cleaved and noncleaved hemojuvelin, as verified by its binding to an uncleaved mutant hemojuvelin. We localized the hemojuvelin binding site on neogenin to the membrane-proximal fifth and sixth FNIII domains and the juxtamembrane linker and showed that a fragment containing only this region binds 2-3 orders of magnitude more tightly than the entire neogenin ectodomain. Binding to the most membrane-proximal region of neogenin may play a role in regulating the levels of soluble and membrane-bound forms of hemojuvelin, which in turn would influence the amount of free BMP-2 available for binding to its receptors and triggering transcription of the hepcidin gene. Our finding that BMP-2 and neogenin bind simultaneously to hemojuvelin raises the possibility that neogenin is part of a multiprotein complex at the hepatocyte membrane involving BMP, its receptors, and hemojuvelin.

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Section: Discussionmentioning

confidence: 99%

Neogenin Interacts with Hemojuvelin through Its Two Membrane-Proximal Fibronectin Type III Domains

et al. 2008

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Section: Introductionmentioning

confidence: 99%

“…RGMs also function as bone morphogenetic protein (BMP) coreceptors, and RGMc is required for BMP-mediated induction of hepcidin, a key regulator of iron homeostasis (Babitt et al, 2006;Xia et al, 2008). Neogenin mediates shedding of RGMc from the cell surface, and soluble RGMc inhibits BMP-induced expression of hepcidin (Babitt et al, 2007;Zhang et al, 2007).Second, although DCC is expressed mainly in the central nervous system (CNS), neogenin is expressed widely during development . In the developing mammary gland, netrin-1 is expressed in preluminal cells and neogenin is expressed in adjacent cap cells of terminal end buds; mice lacking either factor display cell dissociation and tissue disorganization from loss of netrin-1/neogenin adhesive interactions (Srinivasan et al, 2003).…”

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confidence: 99%

Neogenin Regulates Skeletal Myofiber Size and Focal Adhesion Kinase and Extracellular Signal-regulated Kinase Activities In Vivo and In Vitro

Bae

Yang

Jiang

et al. 2009

MBoC

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A variety of signaling pathways participate in the development of skeletal muscle, but the extracellular cues that regulate such pathways in myofiber formation are not well understood. Neogenin is a receptor for ligands of the netrin and repulsive guidance molecule (RGM) families involved in axon guidance. We reported previously that neogenin promoted myotube formation by C2C12 myoblasts in vitro and that the related protein Cdo (also Cdon) was a potential neogenin coreceptor in myoblasts. We report here that mice homozygous for a gene-trap mutation in the Neo1 locus (encoding neogenin) develop myotomes normally but have small myofibers at embryonic day 18.5 and at 3 wk of age. Similarly, cultured myoblasts derived from such animals form smaller myotubes with fewer nuclei than myoblasts from control animals. These in vivo and in vitro defects are associated with low levels of the activated forms of focal adhesion kinase (FAK) and extracellular signal-regulated kinase (ERK), both known to be involved in myotube formation, and inefficient expression of certain muscle-specific proteins. Recombinant netrin-2 activates FAK and ERK in cultured myoblasts in a neogenin-and Cdo-dependent manner, whereas recombinant RGMc displays lesser ability to activate these kinases. Together, netrin-neogenin signaling is an important extracellular cue in regulation of myogenic differentiation and myofiber size. INTRODUCTIONSkeletal muscle is the most abundant tissue, by mass, in the vertebrate body. Muscles of the trunk and limbs arise from the somites, with myogenic progenitor cells derived from the dorsal region of the maturing somite, the dermomyotome (Tajbakhsh and Buckingham, 2000;Pownall et al., 2002;Charge and Rudnicki, 2004). In response to signals from the adjacent notochord, neural tube, and surface ectoderm, some dermomyotomal progenitors become committed to the muscle lineage and form the myotome, a set of differentiated muscle cells that underlies the dermomyotome. Subsequent embryonic, fetal, and postnatal stages of myogenesis are thought to involve additional muscle progenitors that migrate from the dermomyotome and ultimately establish the trunk and limb musculature, as well as satellite cells, adult muscle precursor cells (Gros et al., 2005;Kassar-Duchossoy et al., 2005;Relaix et al., 2005). Somitic progenitor cells are specified to become muscle lineage-committed myoblasts through the action of the myogenic basic helix-loop-helix transcription factors Myf5, MRF4, and MyoD, whereas differentiation of myoblasts is regulated by myogenin, MyoD, and MRF4 (Tajbakhsh, 2005). These and other transcription factors coordinate the process of differentiation, including cell cycle withdrawal, expression of muscle-specific proteins, cellular elongation, and fusion into multinucleated myofibers. Although transcriptional regulation is at the core of myogenesis, the formation and growth of myofibers is also controlled by a variety of signaling ligands and their receptors, including insulin-like growth factor-1, fibroblast growth fac...

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“…All these results demonstrate the essential role of furin in producing s-HJV. The crucial role of furin is further confirmed by the overexpression of the inactive furin variant W547R, 16 which significantly reduced s-HJV release.Since the production of s-HJV is increased in vivo during iron deficiency, 26 we analyzed the furin expression after modulation of cellular iron status. As previously reported, iron addition suppressed s-HJV production, 7,9 but reduced also the amount of furin protein.…”

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confidence: 99%

Furin-mediated release of soluble hemojuvelin: a new link between hypoxia and iron homeostasis

Silvestri

Pagani

Camaschella

2008

Blood

279

276

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The liver peptide hepcidin regulates iron absorption and recycling. Hemojuvelin (HJV) has a key role in hepcidin regulation, and its inactivation causes severe iron overload both in humans and in mice. Membrane HJV (m-HJV) acts as a coreceptor for bone morphogenetic proteins (BMPs), whereas soluble HJV (s-HJV) may down-regulate hepcidin in a competitive way interfering with BMP signaling. s-HJV is decreased by iron in vitro and increased by iron deficiency in vivo. IntroductionThe liver peptide hepcidin is the key regulator of systemic iron homeostasis 1 since it determines the level of circulating iron controlling intestinal iron absorption and macrophage iron recycling. Hemojuvelin (HJV) is a recently recognized protein that plays a crucial role in the regulation of hepcidin. The HJV gene, encoding HJV, is the gene of 1q-linked juvenile hemochromatosis, a recessive disease that leads to severe iron overload of early onset (hemochromatosis type 2A, OMIM no. 602390). 2 Patients with mutated HJV as well as Hjv Ϫ/Ϫ mice 3,4 have low/absent hepcidin levels, indicating that HJV modulates hepcidin. HJV is expressed in liver, skeletal muscle, and heart 2 and belongs to the family of repulsive guidance molecules (RGMs), expressed mainly in the central nervous system. 5,6 As are the other RGM proteins, HJV is characterized by a signal peptide, a RGD motif, a partial von Willebrand factor type D domain, and a glycosilphosphatidylinositol (GPI)-anchor domain. 2 HJV undergoes a partial autocatalytic cleavage 7 to reach the plasma membrane (m-HJV) as a cleaved heterodimer. 8,9 Recently, it was shown that HJV is a coreceptor for bone morphogenetic proteins (BMPs) and that hepcidin regulation occurs via the BMP/SMAD pathway. 10,11 BMP2 and BMP4 signaling is dependent on diferric transferrin, thus establishing a link between HJV-BMP and iron. 12 HJV exists in 2 forms: a membrane-bound (m-HJV) and a soluble one (s-HJV), which in vitro reciprocally regulate hepcidin expression in response to opposite iron changes. 7 s-HJV is able to interfere with and to block the signaling of BMP2 and BMP4 both in vitro 12 and in vivo. 13 We have previously documented the relevance of m-HJV in the molecular pathogenesis of juvenile hemochromatosis, providing evidence that at least some of the mutants identified as causal in patients are less efficiently targeted to the plasma membrane, compared with the wild-type protein. 9 Generation of s-HJV appears to be a regulated process decreased by iron treatment and diferric transferrin. 7 During our previous study, we have confirmed that this regulation is maintained in mutants, strengthening that s-HJV, suppressed by iron overload, is not involved in the disease pathogenesis. 9 We have also suggested that s-HJV does not derive from shedding of m-HJV, since its release in the medium is observed even in mutants that barely reach the plasma membrane. The discrepancy between the presence of m-HJV and the production of s-HJV is also well exemplified by the efficient secretion of soluble forms from varian...

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Evidence That Inhibition of Hemojuvelin Shedding in Response to Iron Is Mediated through Neogenin

Cited by 111 publications

References 41 publications

Neogenin Interacts with Hemojuvelin through Its Two Membrane-Proximal Fibronectin Type III Domains

Neogenin Interacts with Hemojuvelin through Its Two Membrane-Proximal Fibronectin Type III Domains

Neogenin Regulates Skeletal Myofiber Size and Focal Adhesion Kinase and Extracellular Signal-regulated Kinase Activities In Vivo and In Vitro

Furin-mediated release of soluble hemojuvelin: a new link between hypoxia and iron homeostasis

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