RNA silencing of the mitochondrial ABCB7 transporter in HeLa cells causes an iron-deficient phenotype with mitochondrial iron overload (original) (raw)
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Proceedings of the National Academy of Sciences, 2010
The mitochondrion is well known for its key role in energy transduction. However, it is less well appreciated that it is also a focal point of iron metabolism. Iron is needed not only for heme and iron sulfur cluster (ISC)-containing proteins involved in electron transport and oxidative phosphorylation, but also for a wide variety of cytoplasmic and nuclear functions, including DNA synthesis. The mitochondrial pathways involved in the generation of both heme and ISCs have been characterized to some extent. However, little is known concerning the regulation of iron uptake by the mitochondrion and how this is coordinated with iron metabolism in the cytosol and other organelles (e.g., lysosomes). In this article, we discuss the burgeoning field of mitochondrial iron metabolism and trafficking that has recently been stimulated by the discovery of proteins involved in mitochondrial iron storage (mitochondrial ferritin) and transport (mitoferrin-1 and -2). In addition, recent work examining mitochondrial diseases (e.g., Friedreich's ataxia) has established that communication exists between iron metabolism in the mitochondrion and the cytosol. This finding has revealed the ability of the mitochondrion to modulate whole-cell ironprocessing to satisfy its own requirements for the crucial processes of heme and ISC synthesis. Knowledge of mitochondrial ironprocessing pathways and the interaction between organelles and the cytosol could revolutionize the investigation of iron metabolism.
Journal of Biological …, 1999
Nfs1p is the yeast homolog of the bacterial proteins NifS and IscS, enzymes that release sulfur from cysteine for iron-sulfur cluster assembly. Here we show that the yeast mitochondrial protein Nfs1p regulates cellular and mitochondrial iron homeostasis. A strain of Saccharomyces cerevisiae, MA14, with a missense NFS1 allele (I191S) was isolated in a screen for altered iron-dependent gene regulation. This mutant exhibited constitutive up-regulation of the genes of the cellular iron uptake system, mediated through effects on the Aft1p iron-regulatory protein. Iron accumulating in the mutant cells was retained in the mitochondrial matrix while, at the same time, iron-sulfur proteins were deficient. In this work, the yeast protein was localized to mitochondria, and the gene was shown to be essential for viability. Furthermore, Nfs1p in the MA14 mutant was found to be markedly decreased, suggesting that this low protein level produced the observed regulatory effects. This hypothesis was confirmed by experiments in which expression of wild-type Nfs1p from a regulated galactose-induced promoter was turned off, leading to recapitulation of the iron regulatory phenotypes characteristic of the MA14 mutant. These phenotypes include decreases in iron-sulfur protein activities coordinated with increases in cellular iron uptake and iron distribution to mitochondria.
The role of iron in mitochondrial function
Biochimica et Biophysica Acta (BBA) - General Subjects, 2009
Background: Iron is an essential element for life, as it is a cofactor for enzymes involved in many metabolic processes, but it can also be harmful, since its excess is thought to enhance the production of reactive oxygen species and induce oxidative damage. Iron is transformed into its biologically available form in the mitochondrion by the iron-sulfur (Fe/S) cluster and heme synthesis pathways. During the past decade, substantial progress has been made in the elucidation of iron-linked mechanisms that occur in the mitochondrion, demonstrating the crucial role played by this organelle in maintaining cellular iron homeostasis. General Significance: This review summarizes current knowledge of the mechanisms underlying iron trafficking in mitochondria and how it is handled inside the organelle. Relevant updates with regard to the Fe/S cluster and heme biosynthetic pathways, as well as the relationship between mitochondrial iron homeostasis impairment and related diseases, are also discussed.
Evidence for a conserved system for iron metabolism in the mitochondria of Saccharomyces cerevisiae
Proceedings of the National Academy of Sciences, 1999
nifU of nitrogen-fixing bacteria is involved in the synthesis of the Fe-S cluster of nitrogenase. In a synthetic lethal screen with the mitochondrial heat shock protein (HSP)70, SSQ1, we identified a gene of Saccharomyces cerevisiae, NFU1, which encodes a protein with sequence identity to the C-terminal domain of NifU. Two other yeast genes were found to encode proteins related to the N-terminal domain of bacterial NifU. They have been designated ISU1 and ISU2. Isu1, Isu2, and Nfu1 are located in the mitochondrial matrix. ISU genes of yeast carry out an essential function, because a ⌬isu1⌬isu2 strain is inviable. Growth of ⌬nfu1⌬ isu1 cells is significantly compromised, allowing assessment of the physiological roles of Nfu and Isu proteins. Mitochondria from ⌬nfu1⌬isu1 cells have decreased activity of several respiratory enzymes that contain Fe-S clusters. As a result, ⌬nfu1⌬isu1 cells grow poorly on carbon sources requiring respiration. ⌬nfu1⌬isu1 cells also accumulate abnormally high levels of iron in their mitochondria, similar to ⌬ssq1 cells, indicating a role for these proteins in iron metabolism. We suggest that NFU1 and ISU1 gene products play a role in iron homeostasis, perhaps in assembly, insertion, and͞or repair of mitochondrial Fe-S clusters. The conservation of these protein domains in many organisms suggests that this role has been conserved throughout evolution.
Journal of Biological Chemistry, 2005
Two transcriptional activators, Aft1 and Aft2, regulate iron homeostasis in Saccharomyces cerevisiae. These factors induce the expression of iron regulon genes in iron-deficient yeast but are inactivated in iron-replete cells. Iron inhibition of Aft1/Aft2 is abrogated in cells defective for Fe-S cluster biogenesis within the mitochondrial matrix (Chen, O. S., Crisp, R. J., Valachovic, M., Bard, M., Winge, D. R., and Kaplan, J. (2004) J. Biol.
Biochemistry, 2009
Atm1p is an ABC transporter localized in the mitochondrial inner membrane; it functions to export an unknown species into the cytosol and is involved in cellular iron metabolism. Depletion or deletion of Atm1p causes Fe accumulation in mitochondria and a defect in cytosolic Fe/S cluster assembly, but reportedly not a defect in mitochondrial Fe/S cluster assembly. In this study the nature of the accumulated Fe was examined using Mössbauer spectroscopy, EPR, electronic absorption spectroscopy, X-ray absorption spectroscopy, and electron microscopy. The Fe that accumulated in aerobically grown cells was in the form of Fe(III) phosphate nanoparticles similar to that which accumulates in yeast frataxin Yfh1p-deleted or yeast ferredoxin Yah1p-depleted cells. Relative to WT mitochondria, Fe/S cluster and heme levels in Atm1p-depleted mitochondria from aerobic cells were significantly diminished. Atm1p-depletion also caused a build-up of nonheme Fe(II) ions in the mitochondria and an increase in oxidative damage. Atm1p-depleted mitochondria isolated from anaerobically grown cells exhibited WT levels of Fe/S clusters and hemes, and they did not hyperaccumulate Fe. Atm1p-depleted cells lacked Leu1p activity, regardless of whether they were grown aerobically or anaerobically. These results indicate that Atm1p does not participate in mitochondrial Fe/S cluster assembly, and that the species exported by Atm1p is required for cytosolic Fe/S cluster assembly. The Fe/S cluster defect and the Fe-accumulation phenotype, resulting from the depletion of Atm1p in aerobic cells (but not in anaerobic cells), may be secondary effects that are observed only when cells are exposed to oxygen during growth. Reactive oxygen species generated under these conditions might degrade iron-sulfur clusters and lower heme levels in the organelle. Mitochondria play a major role in cellular iron homeostasis, as they are sites where iron is inserted for heme biosynthesis (1) and where iron-sulfur clusters (ISCs) are assembled (2). The ferrous ions used in these processes are imported from the cytosol through the Mrs3p/4p highaffinity inner-membrane (IM) transporters. Some such centers are installed into mitochondrial apo-proteins, and some heme centers are exported to cytosolic targets. The Cytosolic Iron-Sulfur Protein Assembly (CIA) machinery is thought to depend on the mitochondrial ISC machinery, via an arrangement involving the IM protein Atm1p. Atm1p is an ATP Binding Cassette (ABC) "half-transporter" (3) that uses the free energy of ATP hydrolysis to transport an unknown molecular species, termed "X", from the matrix to the intermembrane space (4,
Biophysical Characterization of Iron in Mitochondria Isolated from Respiring and Fermenting Yeast
Biochemistry, 2010
Atm1p is an ABC transporter localized in the mitochondrial inner membrane; it functions to export an unknown species into the cytosol and is involved in cellular iron metabolism. Depletion or deletion of Atm1p causes Fe accumulation in mitochondria and a defect in cytosolic Fe/S cluster assembly, but reportedly not a defect in mitochondrial Fe/S cluster assembly. In this study the nature of the accumulated Fe was examined using Mössbauer spectroscopy, EPR, electronic absorption spectroscopy, X-ray absorption spectroscopy, and electron microscopy. The Fe that accumulated in aerobically grown cells was in the form of Fe(III) phosphate nanoparticles similar to that which accumulates in yeast frataxin Yfh1p-deleted or yeast ferredoxin Yah1p-depleted cells. Relative to WT mitochondria, Fe/S cluster and heme levels in Atm1p-depleted mitochondria from aerobic cells were significantly diminished. Atm1p-depletion also caused a build-up of nonheme Fe(II) ions in the mitochondria and an increase in oxidative damage. Atm1p-depleted mitochondria isolated from anaerobically grown cells exhibited WT levels of Fe/S clusters and hemes, and they did not hyperaccumulate Fe. Atm1p-depleted cells lacked Leu1p activity, regardless of whether they were grown aerobically or anaerobically. These results indicate that Atm1p does not participate in mitochondrial Fe/S cluster assembly, and that the species exported by Atm1p is required for cytosolic Fe/S cluster assembly. The Fe/S cluster defect and the Fe-accumulation phenotype, resulting from the depletion of Atm1p in aerobic cells (but not in anaerobic cells), may be secondary effects that are observed only when cells are exposed to oxygen during growth. Reactive oxygen species generated under these conditions might degrade iron-sulfur clusters and lower heme levels in the organelle.