Granulocyte macrophage colony-stimulating factor and interleukin-5 activate STAT5 and induce CIS1 mRNA in human peripheral blood eosinophils

In these studies, we examined signaling through the transcription factor STAT5 in human peripheral blood eosinophils after treatment with granulocyte macrophage colony-stimulating factor (GM-CSF) or interleukin (IL)-5. In response to either cytokine, STAT5 was rapidly tyrosine phosphorylated and acquired interferon gamma activation site (GAS) DNA binding activity. Tyrosine-phosphorylated STAT5 was associated with both cytosolic and nuclear cell fractions. Consistent with activation, the transcription of a STAT5-dependent gene, cytokine inducible, SH2-containing protein (CIS1), was enhanced after cytokine stimulation. This is the first report of IL-5 regulation of CIS1 gene expression in any cell type. Given its role in cytokine signaling, CIS1 upregulation may serve to attenuate IL-5 and GM-CSF modulation of eosinophil function. These data suggest that active nuclear STAT5 participates in the regulation of IL-5 and GM-CSF-inducible genes in stimulated human peripheral blood eosinophils.