Hematopoietin/Interferon Signaling

1. Hematopoietin/InterferonSignaling Schindler et al pdf

6. JH7 JH6 JH5 JH4 JH3 JH2/yK JH1/TK 500 0 100 600 700 1000 1100 1200 800 300 400 900 200 Expressed in all tissues Expressed in hemato- poietic tissues Janus Kinase Family Tyk2 Jak1 Jak2 Jak3

8. STATs & Four Helix Bundle Cytokines Stat1 IFN-I(,,,) & IFN- Stat2 IFN-I(,,,) Stat3 IL-10 and IL-6 families Stat4 IL-12, IL-23, IL-27 Stat5a/b Single Chain, IL-2 & IL-3 families Stat6 IL-4, IL-13

9. TAD: Transactivation domain; DBD – DNA binding domain

10. Cyt receptor will have at least two JAKs interacting – JAKS will ultimately activate STATs to form either a homo or hetero dimer.

11. Stat1 • Transduces critical signals for all three classes of IFNs. • Stat1 is activated by several other ligands, but its role appears to be more secondary. • Generic biological activities include: • Promoting the expression of inflammatory or “danger” signals. • Antagonizing proliferation and/or promoting apoptosis. • Stat3 appears to antagonize both of these activities. • Stat1 is tyrosine phosphorylated on Y701 and serine phosphorylated on S727 (in the TAD). This latter phosphorylation is required for maximal transcription of some genes. • Stat1 activity is antagonized by phosphatases directed at the receptor and JAKs, and directly by one or more nuclear phosphatases.

12. Stat2 • Transduces critical signals for type I IFNs and -IFNs. • Murine and Human Stat2 are functionally analogous but uncharacteristically divergent in sequence, especially in the TAD. • Stat2 is the only STAT that does not appear to homodimerize and bind DNA directly. • Stat2 activity is antagonized by phosphatases directed at the receptor and JAKs, and directly by one or more nuclear phosphatases. • STAT1/STAT2/IRF9 bind the interferon stimulated response element (ISRE) Murine Coil-Coil DNA SH2 Y689 TAD 923 aa 76 % Homology Divergent Human Coil-Coil DNA SH2 Y690 TAD 851 aa

13. Stat3 • Transduces signals for type I IFNs,-IFNs, the critical signals for the extended IL-10 family and the extended IL-6 families. • Generic biological activities include: • Promoting cell growth associated with cell transformation. • Antagonizing the expression of inflammatory or “danger” signals. • Stat1 antagonizes both of these activities (a ying-yang relationship). • Stat3 is the only STAT that is essential for development (i.e., the knockout is embryonic lethal). Tissues specific knockouts reveal an important roles in protecting tissues form inflammation and suppressing transformation. • Stat3 is tyrosine phosphorylated at Y705, serine phosphorylated at S727 and acetylated at K785. • Stat3 activity is antagonized by phosphatases directed at the receptor and JAKs, and directly by one or more nuclear phosphatases. • Stat3 is important in Th17 development.

14. Stat5a and Stat5b • Transduce critical signals for all members of the IL-2, IL-3 and single chain cytokine receptor families, i.e. is Stat5 is functionally pleiotropic like its ancestral partner Stat3. • Consistent with their significant level of homology, Stat5a & Stat5b can functionally overlap, especially in hematopoietic tissues (e.g., in response to IL-2 and IL-3 family ligands). • However, gene targeting studies have underscored a specificity for Stat5a in prolactin response and a specificity for Stat5b in GH response. • Stat5 has been implicated in the development of some hematopoietic tumors and the regulation of some stem cell populations.

15. Stat4 & Stat6 • Stat4 and Stat6 exhibit a the most ligand specificity. • Stat4 transduces signals for members of the IL-12 family. (IFN-Is can also promote a partial activation of Stat4). • Stat6 transduces signals for closely related IL-4 and IL-13. • Stat4, Stat6 and their activating ligands play an essential role in the development of effector CD4+ T-helper cells. • Stat4 directs the development of Th1 cells – and is involved in expansion of Th17 – through IL-23. • Stat6 directs the development of Th2 cells. • Full Stat4 activation requires both tyrosine phosphorylation at Y689 and serine phosphorylation at S721.

16. Specificity of STATs Determined by inter- vening sequence. STATs usually involved in activation of gene transcription – In many cases, resp. cytokine also induces growth signal – this usually involves other pathways – ex is IRS pathway used by IL-4

17. Regulation of JAK-STAT Suppressor of cytokine signaling (SOCS) Cytokine –inducible SH2 containing protein (CIS) Protein inhibitors of activated STAT (PIAS) Protein phosphatases (PTK)

22. SOCS specificity • Suppressor of Cytokine Signaling 1 (SOCS-1), a Stat1 target gene, directs an important negative feed back loop to suppress IFN-Stat1 dependent signals. • SOCS-2 specifically antagonizes Stat5b activation in response to GH (i.e., SOCS-2 knockout mice exhibit gigantism). • In response to stimulation by the IL-6 family of ligands, Stat3 activity is directly suppressed by SOCS-3, a Stat3 target gene.

23. Nature Immunology4, 1169 - 1176 (2003)

24. Nature Immunology4, 1169 - 1176 (2003)

25. CIS/SOCS Facts • CIS binds to cytokine receptors—probably competes for STAT binding sites • SOCS proteins bind to JAK kinases – best understood is SOCS1 – which binds and inhibits all of the JAKS • SOCS1 KOs die within three weeks of birth due to overexpression/overactivity of especially gIFN