Steel factor induces serine phosphorylation of Stat3 in human growth factor-dependent myeloid cell lines.
Steel factor (SLF) acts synergistically with various hematopoietic growth factors that use the Jak-Stat pathways in vivo and in vitro, although the contribution by SLF to this pathway is unknown. We show here that SLF induces time- and dose-dependent phosphorylation of Stat3 in the human growth factor-dependent cell lines MO7e and TF-1. This phosphorylation occurs exclusively on serine residues. Simultaneous stimulation with SLF plus other cytokines that induce tyrosine phosphorylation of Stat3, such as interleukin-9 (IL-9) in MO7e cells or IL-6 in TF-1 cells, resulted in tyrosine phosphorylation and enhanced serine phosphorylation of Stat3. Serine phosphorylation alone did not promote nuclear translocation or DNA binding activity to the sis-inducible element of Stat3. However, costimulation with SLF plus IL-9 in MO7e cells resulted in the nuclear translocation of serine- hyperphosphorylated Stat3. Serine phosphorylation of Stat3 was also observed by the stimulation of cells with granulocyte-macrophage colony- stimulating factor and IL-3, which do not induce tyrosine phosphorylation of Stat3. These results suggest that SLF might modulate the Jak-Stat3 pathway by serine phosphorylation and that the Jak-Stat pathway may be differentially regulated by the combinational stimulation of two or more cytokines.[1]References
- Steel factor induces serine phosphorylation of Stat3 in human growth factor-dependent myeloid cell lines. Gotoh, A., Takahira, H., Mantel, C., Litz-Jackson, S., Boswell, H.S., Broxmeyer, H.E. Blood (1996) [Pubmed]
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