Regulation Of Ferritin Synthesis Research Articles

Hereditary Hyperferritinemia.

Ferritin is a ubiquitous protein that is present in most tissues as a cytosolic protein. The major and common role of ferritin is to bind Fe2+, oxidize it and sequester it in a safe form in the cell, and to release iron according to cellular needs. Ferritin is also present at a considerably low proportion in normal mammalian sera and is relatively iron poor compared to tissues. Serum ferritin might provide a useful and convenient method of assessing the status of iron storage, and its measurement has become a routine laboratory test. However, many additional factors, including inflammation, infection, metabolic abnormalities, and malignancy-all of which may elevate serum ferritin-complicate interpretation of this value. Despite this long history of clinical use, fundamental aspects of the biology of serum ferritin are still unclear. According to the high number of factors involved in regulation of ferritin synthesis, secretion, and uptake, and in its central role in iron metabolism, hyperferritinemia is a relatively common finding in clinical practice and is found in a large spectrum of conditions, both genetic and acquired, associated or not with iron overload. The diagnostic strategy to reveal the cause of hyperferritinemia includes family and personal medical history, biochemical and genetic tests, and evaluation of liver iron by direct or indirect methods. This review is focused on the forms of inherited hyperferritinemia with or without iron overload presenting with normal transferrin saturation, as well as a step-by-step approach to distinguish these forms to the acquired forms, common and rare, of isolated hyperferritinemia.

Iron regulatory protein‐independent regulation of ferritin synthesis by nitrogen monoxide

The discovery of iron-responsive elements (IREs), along with the identification of iron regulatory proteins (IRP1, IRP2), has provided a molecular basis for our current understanding of the remarkable post-transcriptional regulation of intracellular iron homeostasis. In iron-depleted conditions, IRPs bind to IREs present in the 5'-UTR of ferritin mRNA and the 3'-UTR of transferrin receptor (TfR) mRNA. Such binding blocks the translation of ferritin, the iron storage protein, and stabilizes TfR mRNA, whereas the opposite scenario develops when iron in the intracellular transit pool is plentiful. Nitrogen monoxide (commonly designated nitric oxide; NO), a gaseous molecule involved in numerous functions, is known to affect cellular iron metabolism via the IRP/IRE system. We previously demonstrated that the oxidized form of NO, NO(+), causes IRP2 degradation that is associated with an increase in ferritin synthesis [Kim, S & Ponka, P (2002) Proc Natl Acad Sci USA99, 12214-12219]. Here we report that sodium nitroprusside (SNP), an NO(+) donor, causes a dramatic and rapid increase in ferritin synthesis that initially occurs without changes in the RNA-binding activities of IRPs. Moreover, we demonstrate that the translational efficiency of ferritin mRNA is significantly higher in cells treated with SNP compared with those incubated with ferric ammonium citrate, an iron donor. Importantly, we also provide definitive evidence that the iron moiety of SNP is not responsible for such changes. These results indicate that SNP-mediated increase in ferritin synthesis is, in part, due to an IRP-independent and NO(+)-dependent post-transcriptional, regulatory mechanism.

P050. Iron regulatory protein-independent regulation of ferritin synthesis by nitrogen monoxide

P050. Iron regulatory protein-independent regulation of ferritin synthesis by nitrogen monoxide

Iron at the center of ferritin, metal/oxygen homeostasis and novel dietary strategies

Bioiron - central to respiration, photosynthesis and DNA synthesis and complicated by radical chemistry with oxygen - depends on ferritin, the super family of protein nanocages (maxi-ferritins in humans, animals, plant, and bacteria, and mini-ferritins, also called DPS proteins, in bacteria) for iron and oxygen control. Regulation of ferritin synthesis, best studied in animals, uses DNA transcription and mRNA translation check points. Ferritin is a member of both the "oxidant stress response" gene family that includes thioredoxin reductase and quinine reductase, and a member of the iron responsive gene family that includes ferroportin and mt-aconitase ferritin DNA regulation responds preferentially to oxidant response inducers and ferritin mRNA to iron inducers: heme confers regulator synergy. Ferritin proteins manage iron and oxygen, with ferroxidase sites and iron + oxygen substrates to form mineral of both Fe and O atoms; maxi-ferritins contribute more to cellular iron metabolism and mini-ferritins to stress responses. Iron recovery from ferritin is controlled by gated protein pores, possibly contributing to iron absorption from ferritin, a significant dietary iron source. Ferritin gene regulation is a model for integrating DNA/mRNA controls, while ferritin protein function is central to molecular nutrition cellular metabolism at the crossroads of iron and oxygen in biology.

Ferritin: At the Crossroads of Iron and Oxygen Metabolism

AbstractFor Abstract see ChemInform Abstract in Full Text.

Ferritin: At the Crossroads of Iron and Oxygen Metabolism

Iron and oxygen are central to terrestrial life. Aqueous iron and oxygen chemistry will produce a ferric ion trillions of times less soluble than cell iron concentrations, along with radical forms of oxygen that are toxic. In the physiological environment, many proteins have evolved to transport iron or modulate the redox chemistry of iron that transforms oxygen in useful biochemical reactions. Only one protein, ferritin, evolved to concentrate iron to levels needed in aerobic metabolism. Reversible formation and dissolution of a solid nanomineral-hydrated, iron oxide is the main function of ferritin, which additionally detoxifies excess iron and possibly dioxygen and reactive oxygen. Ferritin is a large multifunctional, multisubunit protein with eight Fe transport pores, 12 mineral nucleation sites and up to 24 oxidase sites that produce mineral precursors from ferrous iron and oxygen. Regulation of ferritin synthesis in animals uses both DNA and mRNA controls and genes encoding two types of related subunits with: 1) catalytically active (H) or 2) inactive (L) oxidase sites. Ferritin with varying H/L ratios is related to cell-specific iron and oxygen homeostasis. H-ferritin oxidase activity accelerates rates of iron mineralization in ferritins and, in animals, ferritin produces H(2)O(2) as a byproduct. Properties of ferritin mRNA and ferritin protein pore structure are new targets for manipulating iron homeostasis. Recent observations of the high bioavailability of iron in soybean ferritin and efficient utilization of soybean and ferritin iron by iron-deficient animals, and of soybean iron by humans with borderline deficiency, indicate a role for ferritin in managing global iron deficiency in humans.

Regulation of Ferritin Synthesis and Iron Regulatory Protein 1 by Oxygen in Mouse Peritoneal Macrophages

Ferritin is an intracellular iron storage protein whose synthesis is regulated post-transcriptionally by a mechanism that involves binding of cytoplasmic iron regulatory protein (IRP) to iron-responsive element (IRE) in the 5′ untranslated region of ferritin mRNA. In this study, we have shown that in mouse peritoneal macrophages, the synthesis of ferritin was enhanced and the IRE binding activity of IRP-1 was diminished when the oxygen tension was decreased. Iron is known to induce ferritin synthesis and even in the presence of a low concentration of iron, synthesis of ferritin was enhanced and the activity of IRP-1 was decreased under hypoxia. The enhanced synthesis of ferritin under hypoxia was abolished by the addition of O−2-generating agents but not H2O2. The decreased activity of IRP-1 under hypoxia was reversed by adding O−2-generating agents. These data suggest that O−2generated in the cell is involved in alterations of ferritin synthesis and the activity of IRP-1 by oxygen.

Effects of the Ferritin Open Reading Frame on Translational Induction by iron

Publisher Summary Ferritin—a multimeric iron-storage protein—is evolutionarily conserved from prokaryotes to eukaryotes. It has been proposed that ferritin acts both to store iron for later use and to defend the cytosol against the generation of potentially toxic free radicals via Fenton oxygen chemistry. The regulation of ferritin synthesis is tightly coupled to changes in intracellular iron concentrations in both cultured cells and model vertebrate organisms. Cells in vertebrate organisms respond to excess iron chiefly by post-transcriptional mechanisms. Factors that modulate the effect of iron on ferritin expression are cytokines, such as interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α), nitric oxide (NO), and oxidative agents. Cytokines such as IL-1β modulate the expression of ferritin in the presence of iron. The regulation is accomplished both by transcriptional and translational mechanisms. There have been numerous reports demonstrating that the effect of ferritin iron-responsive element (IRE) on the iron inducibility of heterologous open reading frames is not as potent as on that of endogenous ferritin mRNAs. The difference in inducibility is accounted for by sequences downstream from the IRE and probably within the ferritin open reading frame (ORF). However, mRNAs that contain the ferritin ORF but lack IRE have little or no iron inducibility. This indicates a requirement for iron-responsive protein (IRP) to bind the IRE, and this interaction serves as the fundamental iron-responsive component of the translational regulatory system for ferritin.

Regulation of Ferritin Synthesis in Macrophages by Oxygen and Sulfhydryl-Reactive Agent

Ferritin synthesis is known to be regulated translationally by specific mRNA-protein interactions between an iron-responsive element (IRE) localized in the 5′ untranslated region of ferritin mRNA and IRE-binding protein (IRE-BP). Binding of IRE-BP to IRE depresses its translation. In the present study, we demonstrated that ferritin synthesis in macrophages is strongly induced under hypoxic conditions by diethylmaleate, a sulfhydryl-reactive agent. The induction by diethylmaleate decreased as the oxygen tension rose. O − 2 is involved in this oxygen effect, because the induction was prevented when O − 2-generating agents were present. Actinomycin D did not inhibit the ferritin synthesis induced by diethylmaleate under hypoxi. These results suggest that O − 2 is ivolved in post-transcriptional regulation of ferritin sythesis.

Iron regulation of ferritin gene expression

Ferritin is a ubiquitous iron-storage protein found in the cells of animals, plants, molds, and bacteria which it protects from toxic intracellular levels of iron. Ferritin stores iron within a hollow protein shell formed by subunits of two types, H and L. The 5' untranslated regions of the two subunit mRNAs contain an almost identical 28-nucleotide sequence which regulates translation by binding to a specific cell sap protein. When cell iron level is low, this repressor protein obstructs translation of stored ferritin mRNAs, whereas increased iron levels release this protein, thus permitting extensive ferritin subunit synthesis to respond rapidly. Similar motifs in the 3' untranslated region of transferrin receptor mRNA interact with this protein to regulate breakdown of the mRNA and thus change the receptor population. Finally, transcription of the H and L genes can be independently increased by iron and other factors. In the case of iron, synthesis of the L-mRNA is increased preferentially since ferritin shells with a preponderance of L-subunits store iron more efficiently. Thus regulation of ferritin synthesis at the translational and transcriptional levels and by transferrin receptor mRNA abundance at the level of breakdown provide a coordinated mechanism for protecting cells against the effects of excess iron.

Regulation of ferritin synthesis in malignant and non-malignant lymphoid cells

The different amounts of H-rich and L-rich isoferritins found in malignant and non malignant lymphoid cells are accompanied by proportional variations in the relative quantity of messenger RNAs for the H and L subunits of ferritin. The correlation between levels of messenger RNAs and proteins suggests that the amount of messenger RNA plays an important role in ferritin biosynthesis in these cells. The enhanced expression of ferritin messenger RNAs in some neoplastic cells is not caused by gross alterations in the structure of ferritin genes.

Iron uptake and regulation of ferritin synthesis by hepatoma cells in hormone-supplemented serum-free media.

Iron, as ferric nitrilotriacetate or ferric ammonium citrate, was administered to rat hepatoma cells (H4AZC2) that were grown in serum-containing media or in hormone-supplemented defined media on collagen matrices. High levels of iron either retarded growth or were cytotoxic, so conditions were established for maximum iron loading where cells survived at near normal growth rates. In all cases, cells exposed to iron produced more ferritin than those grown in its absence, and elevated ferritin levels were paralleled by higher intracellular iron contents. Cells grown in serum-free media, however, took up iron more rapidly than corresponding cells in serum-supplemented media, and intracellular iron and ferritin also reached much higher levels. During exponential growth stages, for example, ferritin levels in iron-stimulated cells were 35-fold greater than those in control cells. These results indicate that transferrin is not required as an iron donor as the inorganic iron was taken up effectively and utilized to stimulate ferritin synthesis. Twenty-four hours after iron administration, endocytotic mechanisms were evident by the appearance of coated vesicles and pits and visible cytoskeletal structures. Subsequently, clusters of iron micelles appeared in the cell. Ferritin isolated from iron-overloaded cells were rich in L-type subunits, but newly synthesized ferritins in iron-stimulated or control cells had almost equivalent amounts of heavy and light subunit constituents.

Translational control of ferritin synthesis by iron in embryonic reticulocytes of the bullfrog.

The regulation of ferritin synthesis by iron was examined in the reticulocytes of bullfrog tadpoles where the induction was 40- to 50-fold, increasing from 0.17 +/- 0.05% of total protein synthesis ([3H]leucine incorporation in cell suspension) to 7.4 +/- 1.6% following intraperitoneal injection of ferric ammonium citrate. No significant difference was observed between the levels of ferritin mRNA in control or iron-induced cells, determined by translation of isolated mRNA in a wheat germ system, demonstrating that ferritin induction by iron occurs by a post-transcriptional mechanism. Total protein synthesis in the wheat germ system was half-saturating at 10 micrograms of mRNA/ml whereas ferritin synthesis increased linearly up to 40 micrograms of mRNA/ml, demonstrating that the ferritin mRNA is translated with high efficiency relative to the total proteins synthesized. Studies with the cap analogue 7-methylguanosine-5'-monophosphate, suggest that cap binding is not directly involved in the high translational efficiency of the ferritin mRNA in the wheat germ system. The results indicate that iron-modulated changes in the availability of ferritin mRNA for translation, coupled with the high translational efficiency of the ferritin message, can account for the induction of ferritin synthesis by iron in embryonic erythroid cells.

Novel mechanism for translational control in regulation of ferritin synthesis by iron.

Poly(A)-containing RNA was isolated from the polyribosomal and post-ribosomal fractions of the livers of normal and iron-treated rats. These RNA fractions were then translated in a wheat germ system to provide a measure of the amount of ferritin mRNA present in each fraction. Following iron administration, there was a 2-fold increase in the amount of ferritin mRNA in the polyribosomal fraction. This increase was not inhibited by prior treatment of the rats with actinomycin D or cordycepin, suggesting a cytoplasmic control mechanism. In normal rats, the post-ribosomal fraction contained an amount of ferritin mRNA equal to that in the polyribosomes. When iron was administered, this untranslated ferritin mRNA became reduced to negligible quantities, thus accounting for the doubling of the ferritin mRNA content of the polyribosomal fraction. A scheme is proposed in which translation of the ferritin mRNA in the post-ribosomal fraction is prevented by adhering ferritin subunits. Iron administration removes this inhibition of the translation of ferritin mRNA by promoting aggregation of these subunits into ferritin.

Regulation of Ferritin Synthesis in Rat Liver

Abstract Ferritin synthesis in rat liver is greatly increased by prior treatment of intact animals with iron salts. Liver slices from treated rats incorporate increased amounts of 14C-leucine into ferritin in vitro, with net synthesis of the protein. Slices of spleen, testis, intestine, and kidney also show increased incorporation following iron. The response of the liver to iron has been studied to determine whether increased transcription of genes and the formation of messenger RNA are involved, or whether control is at a later stage in the biosynthetic pathway. Three lines of evidence support the existence of transcriptional control. (a) Actinomycin D inhibits the response to iron. (b) Iron treatment stimulates incorporation of 14C-orotic acid into a rapidly labeled fraction of liver nuclear RNA. (c) Direct addition of iron to liver slices in vitro has failed to stimulate ferritin synthesis, although 59Fe penetrates liver cells.