Janus kinase family (JAK)

The Janus kinase family (JAK) is a group of non-receptor tyrosine kinases that play crucial roles in cytokine signaling and immune regulation. The family consists of four members: JAK1, JAK2, JAK3, and TYK2. They are named after the two-faced Roman god Janus, reflecting their structure with two near-identical phosphate-transferring domains: one active kinase domain (JH1) and a pseudokinase domain (JH2) that regulates activity. JAKs range from 120-140 kDa and have seven homology domains (JH1-7), including a FERM domain (JH4-JH7) that mediates association with cytokine receptors. JAKs are constitutively associated with the intracellular domains of type I and type II cytokine receptors. They function as signal transducers in the JAK-STAT pathway; upon cytokine binding to receptors, JAKs are activated, phosphorylate the receptors, and create docking sites for signaling molecules, especially STATs, ultimately driving gene transcription.

Other names

JAK1JAK2JAK3TYK2just another kinase 1just another kinase 2

JAK inhibitors block cytokine signaling by inhibiting one or more JAK enzymes, thereby interfering with the JAK-STAT signaling pathway in lymphocytes.