title: Genetic evidence for an additional factor required for erythropoietin-induced signal transduction.
abstract: Erythropoietin (EPO) and its receptor (EPOR) are required for the development of mature erythrocytes. After binding of ligand, the EPOR activates a variety of signaling pathways that ultimately control cellular proliferation, survival, and specific gene expression. Although erythroid progenitors appear to be the principal EPO-responsive cell type in vivo due to the restricted expression of the EPOR, many growth factor-dependent cell lines expressing the EPOR can respond to EPO by activating many or all of these pathways. In the present study, we have identified a cellular context (the interleukin-2 [IL-2]-dependent HT-2 line) in which the EPO stimulation of the EPOR fails to support cellular proliferation, STAT-5 induction, or MAPK activation, despite efficient phosphorylation of the EPOR and JAK2 and inhibition of apoptosis after withdrawal of IL-2. Interestingly, when we fused HT-2 cells expressing the EPOR with Ba/F3 cells in a complementation assay, the resulting hybridomas proliferated and potently activated STAT-5 and MAPK in response to EPO. These data indicate that an unidentified cellular factor is needed to mediate signaling by the EPOR. Moreover, Ba/F3 cells apparently express this factor(s) and somatic fusions can, therefore, confer EPO-responsiveness to HT-2 cells that lack this factor.
authors.affiliation: Gladstone Institute of Virology and Immunology, San Francisco, CA 94141, USA.
authors.forename: S L
authors.initials: SL
authors.lastname: Gaffen
authors.forename: S Y
authors.initials: SY
authors.lastname: Lai
authors.forename: G D
authors.initials: GD
authors.lastname: Longmore
authors.forename: K D
authors.initials: KD
authors.lastname: Liu
authors.forename: M A
authors.initials: MA
authors.lastname: Goldsmith
mesh_terms: D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000502:physiology; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000502:physiology; D004789:Enzyme Activation; D004912:Erythrocytes / Q000502:physiology*; D004921:Erythropoietin / Q000494:pharmacology* / Q000502:physiology; D006801:Humans; D008894:Milk Proteins; D017467:Receptors, Erythropoietin / Q000502:physiology*; D050799:STAT5 Transcription Factor; D015398:Signal Transduction / Q000187:drug effects* / Q000235:genetics*; D015534:Trans-Activators / Q000502:physiology
chemical_list: D004268:DNA-Binding Proteins; D008894:Milk Proteins; D017467:Receptors, Erythropoietin; D050799:STAT5 Transcription Factor; D015534:Trans-Activators; D004921:Erythropoietin; D017871:Calcium-Calmodulin-Dependent Protein Kinases