Jaks and Stats are critical components of many cytokine receptor systems; regulating growth, survival, differentiation, and pathogen resistance. An example of these pathways is shown for the IL-6 (or gp130) family of receptors, which coregulate B cell differentiation, plasmacytogenesis, and the acute phase reaction. Cytokine binding induces receptor dimerization, activating the associated Jaks, which phosphorylate themselves and the receptor. The phosphorylated sites on the receptor and Jaks serve as docking sites for the SH2-containing Stats, such as Stat3, and for SH2-containing proteins and adaptors that link the receptor to MAP kinase, PI3K/Akt, and other cellular pathways.
Phosphorylated Stats dimerize and translocate into the nucleus to regulate target gene transcription. Members of the suppressor of cytokine signaling (SOCS) family dampen receptor signaling via homologous or heterologous feedback regulation. Jaks or Stats can also participate in signaling through other receptor classes, as outlined in the Jak/Stat Utilization Table. Researchers have found Stat3 and Stat5 to be constitutively activated by tyrosine kinases other than Jaks in several solid tumors
The Jak/Stat pathway mediates the effects of cytokines, like erythropoietin, thrombopoietin, and G-CSF, which are protein drugs for the treatment of anemia, thrombocytopenia, and neutropenia, respectively. The pathway also mediates signaling by interferons, which are used as antiviral and antiproliferative agents. Researchers have found that dysregulated cytokine signaling contributes to cancer. Aberrant IL-6 signaling contributes to the pathogenesis of autoimmune diseases, inflammation, and cancers such as prostate cancer and multiple myeloma. Jak inhibitors currently are being tested in models of multiple myeloma. Stat3 can act as an oncogene and is constitutively active in many tumors. Crosstalk between cytokine signaling and EGFR family members is seen in some cancer cells. Research has shown that in glioblastoma cells overexpressing EGFR, resistance to EGFR kinase inhibitors is induced by Jak2 binding to EGFR via the FERM domain of the former [Sci. Signal. (2013) 6, ra55].
Activating Jak mutations are major molecular events in human hematological malignancies. Researchers have found a unique somatic mutation in the Jak2 pseudokinase domain (V617F) that commonly occurs in polycythemia vera, essential thrombocythemia, and idiopathic myelofibrosis. This mutation results in the pathologic activation Jak2, associated with receptors for erythropoietin, thrombopoietin, and G-CSF, which control erythroid, megakaryocytic, and granulocytic proliferation and differentiation. Researchers have also shown that somatic acquired gain-of-function mutations of Jak1 are found in adult T cell acute lymphoblastic leukemia. Somatic activating mutations in Jak1, Jak2, and Jak3 have also been identified in pediatric acute lymphoblastic leukemia (ALL). Furthermore, Jak2 mutations have been detected around pseudokinase domain R683 (R683G or DIREED) in Down syndrome childhood B-ALL and pediatric B-ALL
We would like to thank Prof. Stefan Constantinescu, Ludwig Institute for Cancer Research, Brussels, Belgium for contributing to this diagram.
created November 2002
revised November 2012