This protein is activated through phosphorylation of tyrosine 705, in response to various cytokines and growth factors including interferons, epidermal growth factor (EGF), Interleukin (IL-)5, IL-6, hepatocyte growth factor (HGF), leukemia inhibitory factor (LIF), bone morphogenetic protein 2 (BMP-2), IL-10, and also the hormone leptin.