. 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.
. 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.
|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|
|Doty, Raymond T; Sabo, Kathleen M; Chen, Jing et al. (2010) An all-feline retroviral packaging system for transduction of human cells. Hum Gene Ther 21:1019-27|
|Yang, Zhantao; Philips, John D; Doty, Raymond T et al. (2010) Kinetics and specificity of feline leukemia virus subgroup C receptor (FLVCR) export function and its dependence on hemopexin. J Biol Chem 285:28874-82|
|Quigley, John G; Gazda, Hanna; Yang, Zhantao et al. (2005) Investigation of a putative role for FLVCR, a cytoplasmic heme exporter, in Diamond-Blackfan anemia. Blood Cells Mol Dis 35:189-92|
|Lucas, M Lee; Seidel, Nancy E; Porada, Christopher D et al. (2005) Improved transduction of human sheep repopulating cells by retrovirus vectors pseudotyped with feline leukemia virus type C or RD114 envelopes. Blood 106:51-8|
|Quigley, John G; Yang, Zhantao; Worthington, Mark T et al. (2004) Identification of a human heme exporter that is essential for erythropoiesis. Cell 118:757-66|
|Abkowitz, Janis L; Schaison, Gerard; Boulad, Farid et al. (2002) Response of Diamond-Blackfan anemia to metoclopramide: evidence for a role for prolactin in erythropoiesis. Blood 100:2687-91|
|Price, Mary A; Case, Scott S; Carbonaro, Denise A et al. (2002) Expression from second-generation feline immunodeficiency virus vectors is impaired in human hematopoietic cells. Mol Ther 6:645-52|
|Quigley, J G; Burns, C C; Anderson, M M et al. (2000) Cloning of the cellular receptor for feline leukemia virus subgroup C (FeLV-C), a retrovirus that induces red cell aplasia. Blood 95:1093-9|
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