Abstract
The Janus kinase (JAK)-signal transducers and activators of transcription (STAT) pathway is an important signaling pathway of interferons and cytokines. We examined the activation of STAT proteins induced by interleukin-3 (IL-3), granulocyte-macrophage colony-stimulating factor (GM-CSF), or erythropoietin (EPO) using the human leukemia cell line, UT-7, which requires these cytokines for growth. IL-3, GM-CSF, and EPO induced DNA-binding activity to the oligonucleotides corresponding to the sis-inducible elements (SIE) of c-fos, in addition to the beta-casein promoter (beta-CAP), SIE- and beta-CAP-binding proteins were identical to Stat1alpha and Stat3 complex and to Stat5 protein, respectively. This indicates that IL-3, GM-CSF, and EPO commonly activated Stat1alpha, Stat3, and Stat5 proteins in UT-7. However, EPO hardly activated Stat1alpha and Stat3 in UT-7/GM, which is a subline of UT-7 that grows slightly in response to EPO. Transfection studies revealed that UT-7/GM cells constitutively expressing Stat1alpha, but not Stat3, can grow as well in response to EPO as GM-CSF, suggesting that Stat1alpha is involved in the EPO-induced proliferation of UT-7. Thus, although Stat1alpha, Stat3, and Stat5 proteins are activated by GM-CSF, IL-3, and EPO, our data suggest that each STAT protein has a distinctive role in the actions of cytokines.
Highlights
Cytokines play an important role in the proliferation and differentiation of hematopoietic cells
In this study we demonstrated by means of Electromobility Shift Assay (EMSA) using oligonucleotides corresponding to the sis-inducible elements (SIE) consensus sequence that granulocyte macrophage-colony-stimulating factor (GM-CSF), IL-3, and EPO all activate the three distinct SIE binding complexes in UT-7 cells
These results indicate that GM-CSF, IL-3, and EPO commonly induced the activation of Stat1␣, Stat3, and Stat5 in UT-7
Summary
Cytokines play an important role in the proliferation and differentiation of hematopoietic cells. Sis-inducible elements (SIE) of c-fos do not have this motif, SIE binding complexes are induced by GMCSF in the human monocytic leukemia cell line, U937 [17] This suggested that GM-CSF induces the activation of Stat1␣ and Stat proteins, because the SIE consensus sequence is recognized by Stat1␣ and Stat complex. GM-CSF and IL-3 activate Stat1␣ protein in human eosinophils [18], and these cytokines activate Stat or Stat proteins in COS cells reconstituted with the receptors for these cytokines [19, 20]. Both Stat1␣ and Stat are activated by EPO in the murine EPO-dependent cell line, HCD-57 [21]. We examined the role of Stat1␣ and Stat in the EPO-induced cellular proliferation using UT-7 and its subline, UT-7/GM
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