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 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.
Menon
Madhu P
MP
Program in Stem Cell Biology, Maine Medical Center Research Institute, 81 Research Dr, Scarborough, ME 04074, USA.
Fang
Jing
J
Wojchowski
Don M
DM
D000818:Animals; D001854:Bone Marrow Cells / Q000166:cytology; D002478:Cells, Cultured; D004900:Erythroblasts / Q000166:cytology / Q000502:physiology*; D005434:Flow Cytometry; D005786:Gene Expression Regulation; D051379:Mice; D018345:Mice, Knockout; D017467:Receptors, Erythropoietin / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D012156:Reticulocytes / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D013234:Stem Cells / Q000166:cytology*
D017467:Receptors, Erythropoietin