Signal transducer and activator of transcription 5A, Stat5A
The stat proteins function both as cytoplasmic signal transducers and as activators of transcription. Stat5 is activated in response to a wide variety of ligands including IL-2, GM-CSF, growth hormone, and prolactin. Phosphorylation at Tyr-694 is required for Stat5A activation. Stat5 has been found to be 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. Both Stat5A (Tyr-694) and Stat5B (Tyr-699) are independently regulated and activated in various cell types. For instance, both isoforms are activated in response to IFNalpha in B cells, but only Stat5A is phosphorylated in response to IFNalpha in HeLa cells.
