title: Attenuated signaling by a phosphotyrosine-null Epo receptor form in primary erythroid progenitor cells.
abstract: Signals provided by the erythropoieitin receptor (EpoR) are required for erythroid development beyond the erythroid colony-forming unit (CFU-e) stage and are propagated via the EpoR-tethered Janus kinase, JAK2. JAK2 functions, in part, to phosphorylate 8 conserved EpoR phosphotyrosine (PY) sites for the binding of a diverse set of signaling factors. However, recent studies in transgenic and knock-in mice have demonstrated substantial bioactivity for PY-null EpoR forms. Presently, the activities of a PY-null EpoR-HM form in primary progenitor cells from knock-in mice were further assessed using optimized Epo dose-dependent proliferation, survival, and differentiation assays. As compared with the wild-type (wt)-EpoR, EpoR-HM activity was compromised several-fold in each context when Epo was limited to physiologic concentrations. Possible compensatory increases in serum growth factor levels also were investigated, and as assayed using embryonic stem (ES) cell-derived erythroid G1E2 cells, activities in serum from EpoR-HM mice were substantially elevated. In addition, when challenged with phenylhydrazine-induced anemia, EpoR-HM mice failed to respond with efficient splenic stress erythropoiesis. Thus, the function of this JAK2-coupled but minimal PY-null EpoR-HM form appears to be attenuated in several contexts and to be assisted in vivo by compensatory mechanisms. Roles normally played by EpoR PY sites and distal domains therefore should receive continued attention.
authors.affiliation: Immunobiology Program and Department of Veterinary Science, The Pennsylvania State University, University Park, PA 16802, USA.
authors.forename: Ke
authors.initials: K
authors.lastname: Li
authors.forename: Madhu P
authors.initials: MP
authors.lastname: Menon
authors.forename: Vinit G
authors.initials: VG
authors.lastname: Karur
authors.forename: Shailaja
authors.initials: S
authors.lastname: Hegde
authors.forename: Don M
authors.initials: DM
authors.lastname: Wojchowski
mesh_terms: D000740:Anemia / Q000139:chemically induced; D000818:Animals; D001854:Bone Marrow Cells; D002454:Cell Differentiation / Q000187:drug effects / Q000235:genetics; D002455:Cell Division / Q000187:drug effects / Q000235:genetics; D002470:Cell Survival / Q000187:drug effects / Q000235:genetics; D015672:Erythroid Precursor Cells / Q000166:cytology*; D004920:Erythropoiesis; D004921:Erythropoietin / Q000494:pharmacology; D053614:Janus Kinase 2; D051379:Mice; D008822:Mice, Transgenic; D019000:Phosphotyrosine / Q000235:genetics*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D017467:Receptors, Erythropoietin / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D013154:Spleen / Q000166:cytology / Q000502:physiology
chemical_list: D011518:Proto-Oncogene Proteins; D017467:Receptors, Erythropoietin; D004921:Erythropoietin; D019000:Phosphotyrosine; D011505:Protein-Tyrosine Kinases; C507926:Jak2 protein, mouse; D053614:Janus Kinase 2