title: Stem cell factor enhances erythropoietin-mediated transactivation of signal transducer and activator of transcription 5 (STAT5) via the PKA/CREB pathway.
abstract: OBJECTIVE
  To define whether the observed synergistic effects of erythropoietin (EPO) and stem cell factor (SCF) on erythroid cells can, in part, be mediated by the signal transducer and activator of transcription 5 (STAT5).
  
  
  METHODS
  STAT5 activation was examined in erythroid cell lines by analyzing the effects of EPO and SCF on STAT5 tyrosine phosphorylation, serine phosphorylation, DNA binding, and STAT5-mediated gene transactivation.
  
  
  RESULTS
  EPO induced a 5.0-fold+/-0.4-fold increase in STAT5 transactivation, which could be further enhanced by SCF. SCF pretreatment followed by EPO stimulation resulted in a 9.0-fold+/-0.9-fold increase in STAT5 transactivation, while SCF alone did not increase STAT5 transactivation. This costimulatory effect of SCF was not mediated by increased STAT5 tyrosine or serine phosphorylation or increased STAT5 DNA binding. In addition, enhanced STAT5 transactivation was independent of the phosphatidyl inositol 3-kinase and MAPK(p42/p44) pathways. Instead, the protein kinase A (PKA) inhibitor protein PKI and the PKA inhibitor H89 prevented the costimulatory SCF effect. Furthermore, the PKA target CREB showed a strongly increased and prolonged serine-133 phosphorylation after costimulation with SCF + EPO. The involvement of CREB in STAT5 transactivation was demonstrated by overexpression of serine-133-mutated CREB, which completely blocked the SCF effect. In addition, the CREB-binding protein CBP/p300 was shown to be essential for EPO- and SCF-mediated STAT5 transactivation.
  
  
  CONCLUSIONS
  SCF enhances the EPO-mediated STAT5 transactivation by triggering a PKA/CREB-dependent pathway.
authors.affiliation: Division of Hematology, Department of Medicine, University Hospital Groningen, Hanzeplein 1, 9713 GZ Groningen, The Netherlands.
authors.forename: Arjen-Kars
authors.initials: AK
authors.lastname: Boer
authors.forename: A Lyndsay
authors.initials: AL
authors.lastname: Drayer
authors.forename: Edo
authors.initials: E
authors.lastname: Vellenga
mesh_terms: D050882:CREB-Binding Protein; D002460:Cell Line; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000096:biosynthesis* / Q000187:drug effects; D004357:Drug Synergism; D004921:Erythropoietin / Q000494:pharmacology*; D006801:Humans; D008894:Milk Proteins; D009687:Nuclear Proteins / Q000502:physiology; D010766:Phosphorylation; D050799:STAT5 Transcription Factor; D015398:Signal Transduction; D019089:Stem Cell Factor / Q000494:pharmacology*; D015534:Trans-Activators / Q000096:biosynthesis* / Q000187:drug effects / Q000502:physiology; D015533:Transcriptional Activation / Q000187:drug effects*
chemical_list: D017362:Cyclic AMP Response Element-Binding Protein; D004268:DNA-Binding Proteins; D008894:Milk Proteins; D009687:Nuclear Proteins; D050799:STAT5 Transcription Factor; D019089:Stem Cell Factor; D015534:Trans-Activators; D004921:Erythropoietin; D004247:DNA; D050882:CREB-Binding Protein; C494363:CREBBP protein, human; D017868:Cyclic AMP-Dependent Protein Kinases