Figure 2. Impaired STAT3 function affects multiple pathways. (A) A wide range of cytokines and growth factors activate receptors utilizing the tyrosine kinases JAK2 and Tyk2 which trigger signaling pathways involving STAT3. Phosphorylated STAT3 can homo- or heterodimerize with other STAT3 molecules or STAT1 or STAT5, respectively. STAT complexes modulate transcription of various genes, including increased IL-6, IL-10, IL-17A/17F, IL-22, TGFβ, MCP1 production, as well as decreased TNFα, IL-12 and IFNγ synthesis. (B) Mutations in STAT3 molecules can lead to dominant negative effects of the molecules, hence reducing or abolishing STAT3-dependent activities.