scholarly journals Haem inhibits iron uptake subsequent to endocytosis of transferrin in reticulocytes

1988 ◽  
Vol 251 (1) ◽  
pp. 105-109 ◽  
Author(s):  
P Ponka ◽  
H M Schulman ◽  
J Martinez-Medellin
Keyword(s):  
Iron Uptake ◽  
Initial Rate ◽  
Secondary Effect ◽  
Erythroid Cells ◽  
Iron Incorporation ◽  
Low Concentrations ◽  
High Concentrations ◽  
Transferrin Uptake ◽  
In Erythroid Cells

Haem controls the rate of haem synthesis in erythroid cells by inhibiting iron incorporation from transferrin. The present results indicate that haem primarily inhibits the release of iron from transferrin subsequent to transferrin endocytosis and that the inhibition of transferrin endocytosis caused by relatively high concentrations of haem is a secondary effect. Low concentrations of haem (10-25 microM) significantly inhibit reticulocyte iron uptake and to a greater extent its incorporation into haem, but do not inhibit either the initial rate of transferrin uptake or its internalization by the cells.

Transcriptional Regulation of Transferrin Receptor by Heme in Erythroid Cells

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 2049-2049
Author(s):  
Matthias Schranzhofer ◽  
Nam-Chun Lok ◽  
Manfred Schifrer ◽  
Ernst W Muellner ◽  
Prem Ponka
Keyword(s):  
Mrna Stability ◽  
Aminolevulinic Acid ◽  
Conflicts Of Interest ◽  
Erythroid Cells ◽  
Knock Out ◽  
Iron Regulatory Proteins ◽  
Iron Incorporation ◽  
Knock Out Mice ◽  
Feedback Regulator ◽  
In Erythroid Cells

Abstract Abstract 2049 Erythroid cells are the largest consumers of iron which is delivered to them by tansferrin (Tf) by its cognate receptor (TfR). In contrast to other cells, developing red blood cells (RBC) regulate TfR expression not only at the level of mRNA stability via the iron regulatory proteins (IRP) 1 and 2, but also by transcription (Lok & Ponka, J Biol Chem 275:24185-90, 2000). Here we provide evidence that TfR expression and cellular uptake of iron from Tf is stimulated by enhanced heme synthesis. Incubation of erythroid cells with 5-aminolevulinic acid (ALA) increased TfR expression accompanied by increased iron incorporation into heme. This effect of ALA can be completely prevented by the inhibitors of heme biosynthesis (succinylacetone [blocks ALA dehydratase] or N-methylprotoporphyrin [blocks ferrochelatase]), indicating that the effect of ALA requires its metabolism to heme. The induction of TfR mRNA expression by ALA is mainly a result of increased mRNA synthesis since the effect of ALA can be abolished by actinomycin D. Recently, IRP2 was proposed to play a role in maintaining TfR mRNA stability in developing RBC (Cooperman et al., Blood 106:1084-91; 2005; Galy et al., Blood 106:2580-9, 2005). Importantly, we have demonstrated that ALA added to cultures of erythroid cells derived from IRP2 knock out mice restores the expression of TfR to levels observed in cells obtained from wild type mice. In conclusion, our results indicate that in erythroid cells heme serves as a positive feedback regulator that maintains high TfR levels thus ensuring adequate iron availability for hemoglobin synthesis. Disclosures: No relevant conflicts of interest to declare.

scholarly journals Regulation of heme synthesis in erythroid cells: hemin inhibits transferrin iron utilization but not protoporphyrin synthesis

Blood ◽  
1985 ◽  
Vol 65 (4) ◽  
pp. 850-857 ◽  
Author(s):  
P Ponka ◽  
HM Schulman
Keyword(s):  
Biosynthetic Pathway ◽  
Aminolevulinic Acid ◽  
Cell Uptake ◽  
Erythroid Cell ◽  
Transferrin Receptors ◽  
Erythroid Cells ◽  
Heme Synthesis ◽  
High Concentrations ◽  
In Erythroid Cells

Abstract The inhibition of delta-aminolevulinic acid (ALA) synthase activity by heme is commonly thought to regulate the overall rate of heme synthesis in erythroid cells. However, since heme inhibits erythroid cell uptake of iron from transferrin, we have tested the hypothesis that in reticulocytes heme regulates its own synthesis by controlling the cellular acquisition of iron from transferrin rather than by controlling the synthesis of ALA. We found that hemin added to reticulocytes in vitro inhibits not only the total cell incorporation of 59Fe from transferrin but also the incorporation of [2–14C]-glycine and transferrin-bound 59Fe into heme. However, hemin did not inhibit [2 –14C]-glycine incorporation into protoporphyrin. Furthermore, cycloheximide, which increases the level of non-hemoglobin heme in reticulocytes, also inhibited [2–14C]-glycine into heme but not into protoporphyrin. With high concentrations of ferric pyridoxal benzoylhydrazone (Fe-PBH), which, independent of transferrin and transferrin receptors, can be used as a source of iron for heme synthesis in reticulocytes, significantly more iron is incorporated into heme than from saturating concentrations of Fe-transferrin. This suggests that some step (or steps) in the pathway of iron from extracellular transferrin to protoporphyrin limits the overall rate of heme synthesis in reticulocytes. In addition, hemin in concentrations that inhibit the utilization of transferrin-bound iron for heme synthesis has no effect on the incorporation of iron from Fe-PBH into heme. Our results indicate that in reticulocytes heme inhibits and controls the utilization of iron from transferrin but has no effect on the enzymes of porphyrin biosynthesis and ferrochelatase. This mode of regulation of heme synthesis may be a specific characteristic of the hemoglobin biosynthetic pathway.

scholarly journals Inhibition by oxalomalate of rat liver mitochondrial and extramitochondrial aconitate hydratase

1971 ◽  
Vol 125 (2) ◽  
pp. 557-562 ◽  
Author(s):  
A. Adinolfi ◽  
V. Guarriera-Bobyleva ◽  
S. Olezza ◽  
A. Ruffo
Keyword(s):  
Rat Liver ◽  
Initial Rate ◽  
Competitive Inhibition ◽  
Liver Mitochondria ◽  
Rat Liver Mitochondria ◽  
Mitochondrial Enzyme ◽  
Aconitate Hydratase ◽  
Inhibited Oxidation ◽  
Low Concentrations ◽  
High Concentrations

1. The effect of oxalomalate on the oxidation of citrate and cis-aconitate in rat liver mitochondria, and on the activity of mitochondrial and cytoplasmic aconitate hydratase, has been investigated. 2. Oxalomalate that was added to intact rat liver mitochondria at high concentrations (2mm) produced complete inhibition of citrate and cis-aconitate oxidation, but lower concentrations (0.1–0.25mm) inhibited oxidation of citrate more than that of cis-aconitate. 3. Aconitate hydratase that was either extracted from mitochondria or soluble in the cytoplasm, was strongly inhibited by low concentrations of oxalomalate (0.01–0.2mm), the mitochondrial enzyme being more sensitive than the soluble one. 4. Oxalomalate, when added together with citrate, produced competitive inhibition; the Ki values calculated were 1×10−6m for the mitochondrial and 2.5×10−6m for the cytoplasmic enzyme. 5. With both the enzymic preparations oxalomalate added together with the substrates inhibited the initial rate of the reaction citrate→cis-aconitate more than that of the reaction isocitrate→cis-aconitate. 6. After 2min of preincubation of the inhibitor with either of the enzymic preparations the inhibition increased tenfold and became irreversible; under these conditions both the reactions were inhibited to the same extent. 7. The inhibition by oxalomalate of aconitate hydratase appeared to be similar in many respects to that produced by fluorocitrate on the same enzyme.

scholarly journals Regulation of heme synthesis in erythroid cells: hemin inhibits transferrin iron utilization but not protoporphyrin synthesis

Blood ◽  
1985 ◽  
Vol 65 (4) ◽  
pp. 850-857 ◽  
Author(s):  
P Ponka ◽  
HM Schulman
Keyword(s):  
Biosynthetic Pathway ◽  
Aminolevulinic Acid ◽  
Cell Uptake ◽  
Erythroid Cell ◽  
Transferrin Receptors ◽  
Erythroid Cells ◽  
Heme Synthesis ◽  
High Concentrations ◽  
In Erythroid Cells

The inhibition of delta-aminolevulinic acid (ALA) synthase activity by heme is commonly thought to regulate the overall rate of heme synthesis in erythroid cells. However, since heme inhibits erythroid cell uptake of iron from transferrin, we have tested the hypothesis that in reticulocytes heme regulates its own synthesis by controlling the cellular acquisition of iron from transferrin rather than by controlling the synthesis of ALA. We found that hemin added to reticulocytes in vitro inhibits not only the total cell incorporation of 59Fe from transferrin but also the incorporation of [2–14C]-glycine and transferrin-bound 59Fe into heme. However, hemin did not inhibit [2 –14C]-glycine incorporation into protoporphyrin. Furthermore, cycloheximide, which increases the level of non-hemoglobin heme in reticulocytes, also inhibited [2–14C]-glycine into heme but not into protoporphyrin. With high concentrations of ferric pyridoxal benzoylhydrazone (Fe-PBH), which, independent of transferrin and transferrin receptors, can be used as a source of iron for heme synthesis in reticulocytes, significantly more iron is incorporated into heme than from saturating concentrations of Fe-transferrin. This suggests that some step (or steps) in the pathway of iron from extracellular transferrin to protoporphyrin limits the overall rate of heme synthesis in reticulocytes. In addition, hemin in concentrations that inhibit the utilization of transferrin-bound iron for heme synthesis has no effect on the incorporation of iron from Fe-PBH into heme. Our results indicate that in reticulocytes heme inhibits and controls the utilization of iron from transferrin but has no effect on the enzymes of porphyrin biosynthesis and ferrochelatase. This mode of regulation of heme synthesis may be a specific characteristic of the hemoglobin biosynthetic pathway.

Characterization of the iron transporter DMT1 (NRAMP2/DCT1) in red blood cells of normal and anemic mk/mkmice

Blood ◽  
2001 ◽  
Vol 98 (13) ◽  
pp. 3823-3830 ◽  
Author(s):  
François Canonne-Hergaux ◽  
An-Sheng Zhang ◽  
Prem Ponka ◽  
Philippe Gros
Keyword(s):  
Iron Uptake ◽  
Iron Acquisition ◽  
Uptake System ◽  
Erythroid Cells ◽  
Iron Release ◽  
Loss Of Function ◽  
Divalent Metal Transporter 1 ◽  
Peripheral Tissues ◽  
Divalent Metal Transporter ◽  
In Erythroid Cells

Abstract Divalent metal transporter 1 (DMT1) is the major transferrin-independent iron uptake system at the apical pole of intestinal cells, but it may also transport iron across the membrane of acidified endosomes in peripheral tissues. Iron transport and expression of the 2 isoforms of DMT1 was studied in erythroid cells that consume large quantities of iron for biosynthesis of hemoglobin. In mk/mk mice that express a loss-of-function mutant variant of DMT1, reticulocytes have a decreased cellular iron uptake and iron incorporation into heme. Interestingly, iron release from transferrin inside the endosome is normal in mk/mkreticulocytes, suggesting a subsequent defect in Fe++ transport across the endosomal membrane. Studies by immunoblotting using membrane fractions from peripheral blood or spleen from normal mice where reticulocytosis was induced by erythropoietin (EPO) or phenylhydrazine (PHZ) treatment suggest that DMT1 is coexpressed with transferrin receptor (TfR) in erythroid cells. Coexpression of DMT1 and TfR in reticulocytes was also detected by double immunofluorescence and confocal microscopy. Experiments with isoform-specific anti-DMT1 antiserum strongly suggest that it is the non–iron-response element containing isoform II of DMT1 that is predominantly expressed by the erythroid cells. As opposed to wild-type reticulocytes, mk/mk reticulocytes express little if any DMT1, despite robust expression of TfR, suggesting a possible effect of the mutation on stability and targeting of DMT1 isoform II in these cells. Together, these results provide further evidence that DMT1 plays a central role in iron acquisition via the transferrin cycle in erythroid cells.

scholarly journals Identification of a ferrireductase required for efficient transferrin-dependent iron uptake in erythroid cells

2005 ◽  
Vol 37 (11) ◽  
pp. 1264-1269 ◽  
Author(s):  
Robert S Ohgami ◽  
Dean R Campagna ◽  
Eric L Greer ◽  
Brendan Antiochos ◽  
Alice McDonald ◽  
...  
Keyword(s):  
Iron Uptake ◽  
Erythroid Cells ◽  
In Erythroid Cells

scholarly journals Calmodulin antagonists inhibit and phorbol esters enhance transferrin endocytosis and iron uptake by immature erythroid cells

Blood ◽  
1985 ◽  
Vol 65 (3) ◽  
pp. 758-763
Author(s):  
D Hebbert ◽  
EH Morgan
Keyword(s):  
Calcium Binding ◽  
Iron Uptake ◽  
Phorbol Esters ◽  
Fetal Liver ◽  
Erythroid Cells ◽  
Inhibitory Effects ◽  
Calmodulin Antagonists ◽  
Kinase C ◽  
Fetal Rat ◽  
Transferrin Uptake

Seven antagonists of the calcium-binding protein calmodulin were found to inhibit iron and transferrin uptake by reticulocytes. This inhibition could be completely accounted for by inhibition of the endocytosis and exocytosis of transferrin. When four of the antagonists were tested with the nucleated erythroid cells from the liver of the fetal rat, inhibition of iron uptake was also observed but at higher concentrations than required for the same degree of inhibition with reticulocytes. The tumor promoters phorbol 12-myristate 13-acetate (PMA) and phorbol 12,13-dibutyrate (PDB) were shown to increase the rates of iron and transferrin uptake by reticulocytes and fetal liver erythroid cells by accelerating the rates of transferrin endocytosis and exocytosis. Since these substances are known to stimulate the calcium-activated enzyme protein kinase C while calmodulin antagonists are inhibitory, it is concluded that this enzyme plays an important role in the endocytosis and intracellular cycling of transferrin, and iron uptake by immature erythroid cells. However, the possibilities that calmodulin is also involved or that the inhibitory effects of the calmodulin antagonists are due to nonspecific actions on the cell membrane cannot be excluded.

scholarly journals Calmodulin antagonists inhibit and phorbol esters enhance transferrin endocytosis and iron uptake by immature erythroid cells

Blood ◽  
1985 ◽  
Vol 65 (3) ◽  
pp. 758-763 ◽  
Author(s):  
D Hebbert ◽  
EH Morgan
Keyword(s):  
Calcium Binding ◽  
Iron Uptake ◽  
Phorbol Esters ◽  
Fetal Liver ◽  
Erythroid Cells ◽  
Inhibitory Effects ◽  
Calmodulin Antagonists ◽  
Kinase C ◽  
Fetal Rat ◽  
Transferrin Uptake

Abstract Seven antagonists of the calcium-binding protein calmodulin were found to inhibit iron and transferrin uptake by reticulocytes. This inhibition could be completely accounted for by inhibition of the endocytosis and exocytosis of transferrin. When four of the antagonists were tested with the nucleated erythroid cells from the liver of the fetal rat, inhibition of iron uptake was also observed but at higher concentrations than required for the same degree of inhibition with reticulocytes. The tumor promoters phorbol 12-myristate 13-acetate (PMA) and phorbol 12,13-dibutyrate (PDB) were shown to increase the rates of iron and transferrin uptake by reticulocytes and fetal liver erythroid cells by accelerating the rates of transferrin endocytosis and exocytosis. Since these substances are known to stimulate the calcium-activated enzyme protein kinase C while calmodulin antagonists are inhibitory, it is concluded that this enzyme plays an important role in the endocytosis and intracellular cycling of transferrin, and iron uptake by immature erythroid cells. However, the possibilities that calmodulin is also involved or that the inhibitory effects of the calmodulin antagonists are due to nonspecific actions on the cell membrane cannot be excluded.

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