Core erythropoietin receptor signals for late erythroblast development

Critical signals for erythroblast formation are transduced by activated, tyrosine-phosphorylated erythropoietin receptor (EpoR) complexes. Nonetheless, steady-state erythropoiesis is supported effectively by EpoR alleles that are deficient in cytoplasmic phosphotyrosine sites. To better define core...

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Bibliographic Details
Published in:Blood 2006-04, Vol.107 (7), p.2662-2672
Main Authors: Menon, Madhu P., Fang, Jing, Wojchowski, Don M.
Format: Article
Language:English
Subjects:
Animals
Biological and medical sciences
Bone Marrow Cells - cytology
Cell differentiation, maturation, development, hematopoiesis
Cell physiology
Cells, Cultured
Erythroblasts - cytology
Erythroblasts - physiology
Flow Cytometry
Fundamental and applied biological sciences. Psychology
Gene Expression Regulation
Hematopoiesis
Mice
Mice, Knockout
Molecular and cellular biology
Receptors, Erythropoietin - deficiency
Receptors, Erythropoietin - genetics
Receptors, Erythropoietin - physiology
Reticulocytes - physiology
Reverse Transcriptase Polymerase Chain Reaction
Signal Transduction
Stem Cells - cytology
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Summary:Critical signals for erythroblast formation are transduced by activated, tyrosine-phosphorylated erythropoietin receptor (EpoR) complexes. Nonetheless, steady-state erythropoiesis is supported effectively by EpoR alleles that are deficient in cytoplasmic phosphotyrosine sites. To better define core EpoR action mechanisms, signaling capacities of minimal PY-null (EpoR-HM) and PY343-retaining (EpoR-H) alleles were analyzed for the first time in bone marrow–derived erythroblasts. Jak2 activation via each allele was comparable. Stat5 (and several Stat5-response genes) were induced via EpoR-H but not via EpoR-HM. Stat1 and Stat3 activation was nominal for all EpoR forms. For both EpoR-HM and EpoR-H, Akt and p70S6-kinase activation was decreased multifold, and JNK activation was minimal. ERKs, however, were hyperactivated uniquely via EpoR-HM. In vivo, Epo expression in EpoR-HM mice was elevated, while Epo-induced reticulocyte production was diminished. In vitro, EpoR-HM erythroblast maturation also was attenuated (based on DNA content, forward-angle light scatter, and hemoglobinization). These EpoR-HM–specific defects were corrected not only upon PY343 site restoration in EpoR-H, but also upon MEK1,2 inhibition. Core EpoR PY site-independent signals for erythroblast formation therefore appear to be Stat5, Stat1, Stat3, p70S6-kinase, and JNK independent, but ERK dependent. Wild-type signaling capacities, however, depend further upon signals provided via an EpoR/PY343/Stat5 axis.
ISSN:0006-4971
1528-0020
DOI:10.1182/blood-2005-02-0684