The JAK (Janus Kinase) family of non-receptor tyrosine kinases includes JAK1, JAK2, JAK3, and TYK2.
JAKs associate with a wide variety of cytokine and growth factor receptors. On receptor activation, JAK dimers promote the phosphorylation of STATs (Signal Transducers and Activators of Transcription).
In turn, STATs regulate the downstream transcription of several target genes.
Mutations in JAK, which may lead to overactive cytokine and growth-factor signaling, have been associated with the Philadelphia-negative myeloproliferative neoplasms polycythemia vera, essential thrombocythemia, and primary myelofibrosis.
In solid tumors, signals transduced via JAK-STAT may promote a variety of biological processes considered hallmarks or enabling characteristics of cancer.