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Ferritin iron regulators, PCBP1 and NCOA4, respond to cellular iron status in developing red cells
Moon-Suhn Ryu1, Kari A Duck1, Caroline C Philpott1
1Genetics and Metabolism Section, Liver Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, USA.
Insights
Developing red blood cells tightly regulate iron uptake and hemoglobin synthesis. Cellular iron levels control key proteins, ensuring proper iron flux and preventing microcytic anemia in developing erythroid cells.
Area of Science:
- Hematology
- Cellular Biology
- Molecular Medicine
Background:
- Developing red blood cells have complex systems for iron uptake, heme synthesis, and hemoglobin formation.
- Poly rC-binding protein (PCBP1) and nuclear coactivator 4 (NCOA4) are crucial for iron flux through ferritin in erythroid cells.
- Dysregulation of these factors leads to microcytic anemia.
Purpose of the Study:
- To investigate the regulation of iron flux by cellular iron levels during erythroid terminal differentiation.
- To elucidate the roles of PCBP1 and NCOA4 in response to varying iron concentrations.
Main Methods:
- Utilized a murine model of ex vivo erythroid terminal differentiation.
- Analyzed protein-protein interactions between PCBP1 and ferritin.
- Assessed the impact of iron levels on PCBP1-ferritin interaction and NCOA4 degradation.
Main Results:
- PCBP1 delivers iron to ferritin via a developmentally regulated, iron-sensitive interaction.
- Iron deprivation enhances PCBP1-ferritin interaction, while iron excess inhibits it.
- NCOA4 activity is also developmentally and iron-regulated, with excess iron triggering its lysosomal degradation via HERC2.
Conclusions:
- Developing red blood cells possess sophisticated mechanisms to control iron flux to mitochondria.
- Cellular iron levels dynamically regulate PCBP1 and NCOA4 activities to maintain iron homeostasis during erythropoiesis.
- These regulatory pathways are essential for preventing iron-related anemias.
Abstract:
Developing red blood cells exhibit multiple, redundant systems for regulating and coordinating the uptake of iron, the synthesis of heme, and the formation of hemoglobin during terminal differentiation. We recently described the roles of poly rC-binding protein (PCBP1) and nuclear coactivator 4 (NCOA4) in mediating the flux of iron through ferritin in developing erythroid cells, with PCBP1, an iron chaperone, delivering iron to ferritin and NCOA4, an autophagic cargo receptor, directing ferritin to the lysosome for degradation and iron release. Ferritin iron flux is critical, as mice lacking these factors develop microcytic anemia. Here we report that these processes are regulated by cellular iron levels in a murine model of ex vivo terminal differentiation. PCBP1 delivers iron to ferritin via a direct protein-protein interaction. This interaction is developmentally regulated, enhanced by iron deprivation, and inhibited by iron excess, both in developing cells and in vitro. NCOA4 activity also exhibited developmental regulation and regulation by cellular iron levels. Excess iron uptake during differentiation triggered lysosomal degradation of NCOA4, which was dependent on the E3 ubiquitin ligase HERC2. Thus, developing red blood cells express a series of proteins that both mediate and regulate the flux of iron to the mitochondria.
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