An Iron-Clad Role for Proteasomal Degradation

Iron homeostasis is essential for life and health. In this issue of Cell Metabolism, Moroishi and colleagues (2011) show that FBXL5, an iron sensor in an ubiquitin ligase complex, keeps cellular iron in balance by promoting the degradation of IRP2 in vivo

Iron and Copper in Mitochondrial Diseases

Transition metals are frequently used as cofactors for enzymes and oxygen-carrying proteins that take advantage of their propensity to gain and lose single electrons. Metals are particularly important in mitochondria, where they play essential roles in the production of ATP and detoxification of reactive oxygen species. At the same time, transition metals (particularly Fe and Cu) can promote the formation of harmful radicals, necessitating meticulous control of metal concentration and subcellular compartmentalization. We summarize our current understanding of Fe and Cu in mammalian mitochondrial biology and discuss human diseases associated with aberrations in mitochondrial metal homeostasis

Draft genome sequence of an enterococcus faecalis strain (24FS) that was isolated from healthy infant feces and exhibits high antibacterial activity, multiple-antibiotic resistance, and multiple virulence factors

Enterococcus faecalis 24FS is a bacteriocin-producing, multiply antibiotic-resistant, and potentially virulent bacterium isolated from healthy infant feces. The draft 2.9-Mb genome sequence revealed 2,968 protein-encoding genes; 11 antibiotic resistance, 8 virulence, and 3 bacteriocin genes; and 2 plasmids, 4 prophages, 30 insertion sequence (IS) elements, 1 transposon, and 1 integron

Comparison of the Interactions of Transferrin Receptor and Transferrin Receptor 2 with Transferrin and the Hereditary Hemochromatosis Protein HFE

The transferrin receptor (TfR) interacts with two proteins important for iron metabolism, transferrin (Tf) and HFE, the protein mutated in hereditary hemochromatosis. A second receptor for Tf, TfR2, was recently identified and found to be functional for iron uptake in transfected cells (Kawabata, H., Germain, R. S., Vuong, P. T., Nakamaki, T., Said, J. W., and Koeffler, H. P. (2000) J. Biol. Chem. 275, 16618-16625). TfR2 has a pattern of expression and regulation that is distinct from TfR, and mutations in TfR2 have been recognized as the cause of a non-HFE linked form of hemochromatosis (Camaschella, C., Roetto, A., Cali, A., De Gobbi, M., Garozzo, G., Carella, M., Majorano, N., Totaro, A., and Gasparini, P. (2000) Nat. Genet. 25, 14-15). To investigate the relationship between TfR, TfR2, Tf, and HFE, we performed a series of binding experiments using soluble forms of these proteins. We find no detectable binding between TfR2 and HFE by co-immunoprecipitation or using a surface plasmon resonance-based assay. The affinity of TfR2 for iron-loaded Tf was determined to be 27 nM, 25-fold lower than the affinity of TfR for Tf. These results imply that HFE regulates Tf-mediated iron uptake only from the classical TfR and that TfR2 does not compete for HFE binding in cells expressing both forms of TfR

Complete genome sequence of Lactobacillus plantarum 10CH, a potential probiotic lactic acid bacterium with potent antimicrobial aActivity

Lactobacillus plantarum 10CH is a bacteriocin-producing potential probiotic lactic acid bacterium (LAB) strain isolated from cheese. Its complete nucleotide sequence shows a single circular chromosome of 3.3 Mb, with a G+C content of 44.51%, a 25-gene plantaricin bacteriocin gene cluster, and the absence of recognized virulence factors. [Abstract copyright: Copyright © 2017 El Halfawy et al.

A Spontaneous, Recurrent Mutation in Divalent Metal Transporter-1 Exposes a Calcium Entry Pathway

Divalent metal transporter-1 (DMT1/DCT1/Nramp2) is the major Fe(2+) transporter mediating cellular iron uptake in mammals. Phenotypic analyses of animals with spontaneous mutations in DMT1 indicate that it functions at two distinct sites, transporting dietary iron across the apical membrane of intestinal absorptive cells, and transporting endosomal iron released from transferrin into the cytoplasm of erythroid precursors. DMT1 also acts as a proton-dependent transporter for other heavy metal ions including Mn(2+), Co(2+), and Cu(2), but not for Mg(2+) or Ca(2+). A unique mutation in DMT1, G185R, has occurred spontaneously on two occasions in microcytic (mk) mice and once in Belgrade (b) rats. This mutation severely impairs the iron transport capability of DMT1, leading to systemic iron deficiency and anemia. The repeated occurrence of the G185R mutation cannot readily be explained by hypermutability of the gene. Here we show that G185R mutant DMT1 exhibits a new, constitutive Ca(2+) permeability, suggesting a gain of function that contributes to remutation and the mk and b phenotypes

The Transferrin Receptor Modulates Hfe-Dependent Regulation of Hepcidin Expression

Hemochromatosis is caused by mutations in HFE, a protein that competes with transferrin (TF) for binding to transferrin receptor 1 (TFR1). We developed mutant mouse strains to gain insight into the role of the Hfe/Tfr1 complex in regulating iron homeostasis. We introduced mutations into a ubiquitously expressed Tfr1 transgene or the endogenous Tfr1 locus to promote or prevent the Hfe/Tfr1 interaction. Under conditions favoring a constitutive Hfe/Tfr1 interaction, mice developed iron overload attributable to inappropriately low expression of the hormone hepcidin. In contrast, mice carrying a mutation that interferes with the Hfe/Tfr1 interaction developed iron deficiency associated with inappropriately high hepcidin expression. High-level expression of a liver-specific Hfe transgene in Hfe−/− mice was also associated with increased hepcidin production and iron deficiency. Together, these models suggest that Hfe induces hepcidin expression when it is not in complex with Tfr1

Mutation of Rubie, a Novel Long Non-Coding RNA Located Upstream of Bmp4, Causes Vestibular Malformation in Mice

Background: The vestibular apparatus of the vertebrate inner ear uses three fluid-filled semicircular canals to sense angular acceleration of the head. Malformation of these canals disrupts the sense of balance and frequently causes circling behavior in mice. The Epistatic circler (Ecl) is a complex mutant derived from wildtype SWR/J and C57L/J mice. Ecl circling has been shown to result from the epistatic interaction of an SWR-derived locus on chromosome 14 and a C57L-derived locus on chromosome 4, but the causative genes have not been previously identified. Methodology/Principal Findings: We developed a mouse chromosome substitution strain (CSS-14) that carries an SWR/J chromosome 14 on a C57BL/10J genetic background and, like Ecl, exhibits circling behavior due to lateral semicircular canal malformation. We utilized CSS-14 to identify the chromosome 14 Ecl gene by positional cloning. Our candidate interval is located upstream of bone morphogenetic protein 4 (Bmp4) and contains an inner ear-specific, long non-coding RNA that we have designated Rubie (RNA upstream of Bmp4 expressed in inner ear). Rubie is spliced and polyadenylated, and is expressed in developing semicircular canals. However, we discovered that the SWR/J allele of Rubie is disrupted by an intronic endogenous retrovirus that causes aberrant splicing and premature polyadenylation of the transcript. Rubie lies in the conserved gene desert upstream of Bmp4, within a region previously shown to be important for inner ear expression of Bmp4. We found that the expression patterns of Bmp4 and Rubie are nearly identical in developing inner ears