Using a fusion protein of the human leukemia inhibitory factor (LIF) receptor, researchers found that its phosphorylation in response to LIF stimulation aligns with MAPK activation, with Ser-1044 identified as a key phosphorylation site. Mutants lacking Ser-1044 showed altered cytokine-stimulated gene expression, highlighting the role of MAPK-mediated phosphorylation in regulating LIFR signaling.