Janus kinase 2

Janus kinase 2 (JAK2) is a non-receptor tyrosine kinase that plays a crucial role in signal transduction for a variety of cellular processes including cell growth, differentiation, and apoptosis. It is a member of the Janus kinase family, named after the two-faced Roman god Janus due to their dual functional domains.

Structure

JAK2 is composed of seven JAK homology (JH) domains. The JH1 domain is the kinase domain, responsible for the enzymatic activity of the protein. The JH2 domain is a pseudo-kinase domain, which regulates the activity of the JH1 domain. The remaining JH3-JH7 domains are involved in binding to cytokine receptors.

Function

JAK2 is activated by a variety of cytokines and growth factors. Upon ligand binding to the receptor, JAK2 is activated through trans-phosphorylation. The activated JAK2 then phosphorylates and activates STAT proteins, which translocate to the nucleus and regulate gene expression.

Clinical significance

Mutations in the JAK2 gene are associated with several diseases, including Polycythemia vera, Essential thrombocythemia, and Primary myelofibrosis. The most common mutation is the JAK2 V617F mutation, which results in constitutive activation of the kinase. This leads to uncontrolled cell proliferation and is a major driver of myeloproliferative neoplasms.

Therapeutic implications

Given its role in disease, JAK2 is a target for therapeutic intervention. Several JAK2 inhibitors, such as Ruxolitinib and Fedratinib, have been developed and approved for the treatment of myeloproliferative neoplasms.

See also

• Janus kinase
• Signal transducer and activator of transcription
• Myeloproliferative neoplasm