. The goal of this project is to define the role of the heme export protein Feline Leukemia Virus, subgroup C, Receptor (FLVCR) and heme signaling in hematopoiesis. Cats viremic with Feline leukemia virus, subgroup C (FeLV-C) down-regulate the cell surface expression of FLVCR and develop a profound macrocytic anemia. Mice in which Flvcr is deleted have a comparable clinical phenotype, and in both species, erythroid differentiation arrests at the CFU-E (colony-forming unit-erythroid)/proerythroblast stage. These data led us to hypothesize that FLVCR protects cells when heme synthesis precedes or exceeds globin synthesis and that if these steps were poorly coordinated, ineffective erythropoiesis and anemia would result. This grant will test our hypothesis by directly measuring free heme in developing erythroid cells with a luciferase reporter containing the MARE sequences (Bach1 binding site) of the ?-globin promoter and by measuring heme-regulated eIF2? kinase (HRI) and eIF2? phosphorylation. We will show that excess heme induces anemia with rescue experiments designed to restore the intracellular free heme balance of Flvcr-deleted mice by decreasing heme synthesis or by increasing heme degradation using methods independent of FLVCR. In studies of rps6+/- mice, we will determine whether this pathophysiology could be relevant to the macrocytic anemia of Diamond Blackfan anemia (results from RPS19 haploinsufficiency, failed ribosome assembly, and slowed translation initiation) and the 5q- myelodysplasia syndrome (acquired RPS14 deletion). We will also define the molecular pathways which trigger erythroid marrow failure by transcriptional profiling. In addition, we will explore the role of FLVCR in other hematopoietic cells using comparable experimental strategies, since our recent data suggest that FLVCR is needed for the maturation of double positive T cells to single positive T cells in thymus and may have a role in megakaryocyte endomitosis. We can thus determine whether these different lineages share regulatory pathways. Together these studies should provide significant insights into heme signaling and toxicities during hematopoietic cell differentiation.

Public Health Relevance

. When mice lack FLVCR, a heme export protein, they develop a severe anemia and macrocytosis (large red cells), akin to children with Diamond Blackfan anemia and adults with myelodysplasia. We will determine how and why the early red cells die and thus will gain insights into the pathophysiology, and potentially the therapy, of these diseases. We should also learn about the shared molecular mechanisms controlling red cell, T cell and platelet production.

National Institute of Health (NIH)
National Heart, Lung, and Blood Institute (NHLBI)
Research Project (R01)
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Special Emphasis Panel (ZRG1-VH-F (02))
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Qasba, Pankaj
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University of Washington
Internal Medicine/Medicine
Schools of Medicine
United States
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Yang, Zhantao; Keel, Siobán B; Shimamura, Akiko et al. (2016) Delayed globin synthesis leads to excess heme and the macrocytic anemia of Diamond Blackfan anemia and del(5q) myelodysplastic syndrome. Sci Transl Med 8:338ra67
Philip, Mary; Chiu, Edison Y; Hajjar, Adeline M et al. (2016) TLR Stimulation Dynamically Regulates Heme and Iron Export Gene Expression in Macrophages. J Immunol Res 2016:4039038
Doty, Raymond T; Phelps, Susan R; Shadle, Christina et al. (2015) Coordinate expression of heme and globin is essential for effective erythropoiesis. J Clin Invest 125:4681-91
Keel, Siobán B; Doty, Raymond; Liu, Li et al. (2015) Evidence that the expression of transferrin receptor 1 on erythroid marrow cells mediates hepcidin suppression in the liver. Exp Hematol 43:469-78.e6
Philip, Mary; Funkhouser, Scott A; Chiu, Edison Y et al. (2015) Heme exporter FLVCR is required for T cell development and peripheral survival. J Immunol 194:1677-85
Egan, Daniel N; Yang, Zhantao; Phillips, John et al. (2015) Inducing iron deficiency improves erythropoiesis and photosensitivity in congenital erythropoietic porphyria. Blood 126:257-61
Byon, John C H; Chen, Jing; Doty, Raymond T et al. (2013) FLVCR is necessary for erythroid maturation, may contribute to platelet maturation, but is dispensable for normal hematopoietic stem cell function. Blood 122:2903-10
Keel, Sioban B; Phelps, Susan; Sabo, Kathleen M et al. (2012) Establishing Rps6 hemizygous mice as a model for studying how ribosomal protein haploinsufficiency impairs erythropoiesis. Exp Hematol 40:290-4
Hromas, Robert; Abkowitz, Janis L; Keating, Armand (2012) Facing the NIH funding crisis: how professional societies can help. JAMA 308:2343-4
Jaacks, Lindsay M; Young, Melissa F; Essley, Bridget V et al. (2011) Placental expression of the heme transporter, feline leukemia virus subgroup C receptor, is related to maternal iron status in pregnant adolescents. J Nutr 141:1267-72

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