This gene encodes a non-receptor tyrosine kinase involved in cytokine and growth factor signaling. The primary isoform contains a FERM domain for erythropoietin receptor association, an SH2 domain for STAT binding, a pseudokinase domain, and a C-terminal kinase domain. Cytokine binding triggers autophosphorylation and activation of this kinase, which then phosphorylates STAT proteins. Growth factors like TGF-beta 1 also activate this kinase, leading to STAT translocation to the nucleus to influence gene transcription. Mutations in this gene are linked to inflammatory diseases and cancers. It is a target of IL6, which regulates immune responses and inflammation. Disruption of the IL6/JAK2/STAT3 pathway causes increased cell proliferation and myeloproliferative neoplasms. A mutation in the pseudokinase domain causes constitutive activation, making it hypersensitive to cytokine signaling. Alternative splicing produces multiple isoforms.