Stat5 is activated in response to a wide variety of ligands including IL-2, GM-CSF, growth hormone and prolactin. Phosphorylation at Tyr694 is obligatory for Stat5 activation . This phosphorylation is mediated by Src upon erythropoietin stimulation. Stat5 is constitutively active in some leukemic cell types. Phosphorylated Stat5 is found in some endothelial cells treated with IL-3, which suggests its involvement in angiogenesis and cell motility.
