Mon1a and FCHO2 are required for maintenance of Golgi architecture.

Mon1a has been shown to function in the endolysosomal pathway functioning in the Mon1-Ccz1 complex and it also acts in the secretory pathway where it interacts with dynein and affects ER to Golgi traffic. Here we show that Mon1a is also required for maintenance of the Golgi apparatus. We identified the F-BAR protein FCHO2 as a Mon1a-interacting protein by both yeast two-hybrid analysis and co-immunoprecipitation.

The mitochondrial iron exporter genes and in yeast are transcriptionally regulated by Aft1 and Yap1.

Budding yeast () responds to low cytosolic iron by up-regulating the expression of iron import genes; iron import can reflect iron transport into the cytosol or mitochondria. Mmt1 and Mmt2 are nuclearly encoded mitochondrial proteins that export iron from the mitochondria into the cytosol. Here we report that and expression is transcriptionally regulated by two pathways: the low-iron-sensing transcription factor Aft1 and the oxidant-sensing transcription factor Yap1.

Altered sterol metabolism in budding yeast affects mitochondrial iron-sulfur (Fe-S) cluster synthesis.

Ergosterol synthesis is essential for cellular growth and viability of the budding yeast , and intracellular sterol distribution and homeostasis are therefore highly regulated in this species. Erg25 is an iron-containing C4-methyl sterol oxidase that contributes to the conversion of 4,4-dimethylzymosterol to zymosterol, a precursor of ergosterol. The gene encodes an endoplasmic reticulum (ER)-associated protein, and here we identified a role for Erg29 in the methyl sterol oxidase step of ergosterol synthesis.

The glucose sensor Snf1 and the transcription factors Msn2 and Msn4 regulate transcription of the vacuolar iron importer gene and iron resistance in yeast.

The budding yeast stores iron in the vacuole, which is a major resistance mechanism against iron toxicity. One key protein involved in vacuolar iron storage is the iron importer Ccc1, which facilitates iron entry into the vacuole. Transcription of the gene is largely regulated by the binding of iron-sulfur clusters to the activator domain of the transcriptional activator Yap5.

Erythropoietin signaling regulates heme biosynthesis.

Heme is required for survival of all cells, and in most eukaryotes, is produced through a series of eight enzymatic reactions. Although heme production is critical for many cellular processes, how it is coupled to cellular differentiation is unknown. Here, using zebrafish, murine, and human models, we show that erythropoietin (EPO) signaling, together with the GATA1 transcriptional target, , regulates heme biosynthesis during erythropoiesis at the outer mitochondrial membrane.

Two novel mutations in TMPRSS6 associated with iron-refractory iron deficiency anemia in a mother and child.

In an iron deficient child, oral iron repeatedly failed to improve the condition. Whole exome sequencing identified one previously reported plus two novel mutation in the TMPRSS6 gene, with no mutations in other iron-associated genes. We propose that these mutations result in a novel variety of iron-refractory iron deficiency anemia.

TMEM14C is required for erythroid mitochondrial heme metabolism.

The transport and intracellular trafficking of heme biosynthesis intermediates are crucial for hemoglobin production, which is a critical process in developing red cells. Here, we profiled gene expression in terminally differentiating murine fetal liver-derived erythroid cells to identify regulators of heme metabolism. We determined that TMEM14C, an inner mitochondrial membrane protein that is enriched in vertebrate hematopoietic tissues, is essential for erythropoiesis and heme synthesis in vivo and in cultured erythroid cells.

Expression of the yeast cation diffusion facilitators Mmt1 and Mmt2 affects mitochondrial and cellular iron homeostasis: evidence for mitochondrial iron export.

Mmt1 and Mmt2 are highly homologous yeast members of the cation diffusion facilitator transporter family localized to mitochondria. Overexpression of MMT1/2 led to changes in cellular metal homeostasis (increased iron sensitivity, decreased cobalt sensitivity, increased sensitivity to copper), oxidant generation, and increased sensitivity to H2O2. The phenotypes due to overexpression of MMT1&2 were similar to that seen in cells with deletions in MRS3 and MRS4, genes that encode the mitochondrial iron importers.

Iron regulatory protein-1 protects against mitoferrin-1-deficient porphyria.

Mitochondrial iron is essential for the biosynthesis of heme and iron-sulfur ([Fe-S]) clusters in mammalian cells. In developing erythrocytes, iron is imported into the mitochondria by MFRN1 (mitoferrin-1, SLC25A37). Although loss of MFRN1 in zebrafish and mice leads to profound anemia, mutant animals showed no overt signs of porphyria, suggesting that mitochondrial iron deficiency does not result in an accumulation of protoporphyrins.

Leishmania-mediated inhibition of iron export promotes parasite replication in macrophages.

Leishmania parasites infect macrophages, cells that play an important role in organismal iron homeostasis. By expressing ferroportin, a membrane protein specialized in iron export, macrophages release iron stored intracellularly into the circulation. Iron is essential for the intracellular replication of Leishmania, but how the parasites compete with the iron export function of their host cell is unknown.

The essential nature of iron usage and regulation.

The facile ability of iron to gain and lose electrons has made iron an important participant in a wide variety of biochemical reactions. Binding of ligands to iron modifies its redox potential, thereby permitting iron to transfer electrons with greater or lesser facility. The ability to transfer electrons, coupled with its abundance, as iron is the fourth most abundant mineral in the earth's crust, have contributed to iron being an element required by almost all species in the six kingdoms of life.

A role for iron-sulfur clusters in the regulation of transcription factor Yap5-dependent high iron transcriptional responses in yeast.

Yeast respond to increased cytosolic iron by activating the transcription factor Yap5 increasing transcription of CCC1, which encodes a vacuolar iron importer. Using a genetic screen to identify genes involved in Yap5 iron sensing, we discovered that a mutation in SSQ1, which encodes a mitochondrial chaperone involved in iron-sulfur cluster synthesis, prevented expression of Yap5 target genes. We demonstrated that mutation or reduced expression of other genes involved in mitochondrial iron-sulfur cluster synthesis (YFH1, ISU1) prevented induction of the Yap5 response.

Murine macrophages response to iron.

Macrophages play a critical role at the crossroad between iron metabolism and immunity, being able to store and recycle iron derived from the phagocytosis of senescent erythrocytes. The way by which macrophages manage non-heme iron at physiological concentration is still not fully understood. We investigated protein changes in mouse bone marrow macrophages incubated with ferric ammonium citrate (FAC 10 μM iron).

Mon1a protein acts in trafficking through the secretory apparatus.

Mon1a was originally identified as a modifier gene of vesicular traffic, as a mutant Mon1a allele resulted in increased localization of cell surface proteins, whereas reduced levels of Mon1a showed decreased secretory activity. Here we show that Mon1a affects different steps in the secretory pathway including endoplasmic reticulum-to-Golgi traffic. siRNA-dependent reduction of Mon1a levels resulted in a delay in the reformation of the Golgi apparatus after Brefeldin A treatment.

Ferroportin-mediated iron transport: expression and regulation.

The distinguishing feature between iron homeostasis in single versus multicellular organisms is the need for multicellular organisms to transfer iron from sites of absorption to sites of utilization and storage. Ferroportin is the only known iron exporter and ferroportin plays an essential role in the export of iron from cells to blood. Ferroportin can be regulated at many different levels including transcriptionally, post-transcriptionally, through mRNA stability and post-translationally, through protein turnover.

The role of ubiquitination in hepcidin-independent and hepcidin-dependent degradation of ferroportin.

The iron exporter ferroportin (Fpn) is essential to transfer iron from cells to plasma. Systemic iron homeostasis in vertebrates is regulated by the hepcidin-mediated internalization of Fpn. Here, we demonstrate a second route for Fpn internalization; when cytosolic iron levels are low, Fpn is internalized in a hepcidin-independent manner dependent upon the E3 ubiquitin ligase Nedd4-2 and the Nedd4-2 binding protein Nfdip-1.