JAKs are activated when cytokines or growth factors bind to their respective receptors on the cell surface. This binding causes receptor dimerization, which brings the JAKs into close proximity, allowing them to phosphorylate each other. This phosphorylation event activates the JAKs, which then phosphorylate specific tyrosine residues on the receptor itself, creating docking sites for downstream signaling molecules such as Signal Transducer and Activator of Transcription (STAT) proteins.
