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Interleukin ( IL)-6-type cytokines have no direct antiviral activity; nevertheless, they display immune-modulatory functions. Oncostatin M ( OSM), a member of the IL-6 family, has recently been shown to induce a distinct number of classical interferon stimulated genes ( ISG). Most of them are involved in antigen processing and presentation. However, induction of retinoic acid-inducible gene ( RIG)-I-like receptors ( RLR) has not been investigated. Here we report that OSM has the capability to induce the expression of the DExD/H-Box RNA helicases RIG-I and melanoma differentiation antigen 5 ( MDA5) as well as of the transcription factors interferon regulatory factor ( IRF)1, IRF7 and IRF9 in primary fibroblasts. Induction of the helicases depends on tyrosine as well as serine phosphorylation of STAT1. Moreover, we could show that the OSM-induced STAT1 phosphorylation is predominantly counter-regulated by a strong STAT3-dependent SOCS3 induction, as Stat3 as well as Socs3 knock-down results in an enhanced and prolonged helicase and IRF expression. Other factors involved in regulation of STAT1 or IRF1 activity, like protein tyrosine phosphatase, non-receptor type 2 ( PTPN2), promyelocytic leukaemia protein ( PML) or small ubiquitin-related modifier 1 ( SUMO1), play a minor role in OSM-mediated induction of RLR. Remarkably, OSM and interferon-γ ( IFN-γ) synergize to mediate transcription of RLR and pre-treatment of fibroblasts with OSM fosters the type I interferon production in response to a subsequent encounter with double-stranded RNA. Together, these findings suggest that the OSM-induced JAK/ STAT1 signalling is implicated in virus protection of non-professional immune cells and may cooperate with interferons to enhance RLR expression in these cells. [ABSTRACT FROM AUTHOR]

The Janus kinase 2 mutant V617F occurs with high frequency in myeloproliferative neoplasms. Further mutations affecting the Janus kinase family have been discovered mostly in leukaemias and in myeloproliferative neoplasms. Owing to their involvement in neoplasia, inflammatory diseases and in the immune response, Janus kinases are promising targets for kinase inhibitor therapy in these disease settings. Various quantitative assays including two newly developed screening assays were used to characterize the function of different small-molecule compounds in cells expressing Jak2V617F. A detailed comparative analysis of different Janus kinase inhibitors in our quantitative assays and the subsequent characterization of additional activities demonstrated for the first time that the most potent Jak2 inhibitor in our study, CEP701, also targets Aurora kinases. CEP701 shows a unique combination of both activities which is not found in other compounds also targeting Jak2. Furthermore, colony forming cell assays showed that Janus kinase 2 inhibitors preferentially suppressed the growth of erythroid colonies, whereas inhibitors of Aurora kinases preferentially blocked myeloid colony growth. CEP701 demonstrated a combined suppression of both colony types. Moreover, we show that combined application of a Janus and an Aurora kinase inhibitor recapitulated the effect observed for CEP701 but might allow for more flexibility in combining both activities in clinical settings, e.g. in the treatment of myeloproliferative neoplasms. The newly developed screening assays are high throughput compatible and allow an easy detection of new compounds with Janus kinase 2 inhibitory activity. [ABSTRACT FROM AUTHOR]

• Introduction - Jaks in disease - Jak2-V617F signal transduction • Structure/function: the potential interest of the Jak domains as drug targets - The FERM domain - The FERM domain as drug target - The SH2 domain - The SH2 domain as drug target - The pseudokinase domain - The pseudokinase domain as drug target - The kinase domain - The kinase domain as drug target - Summary • The growing family of ATP-competitive nanomolar Jak inhibitors • Analogue-sensitive kinases and possible applications to Jaks - Chemical genetics to characterize kinases - Chemical genetics in practice: possible pitfalls and requirements - Advantages and possible applications of the chemical genetics approach - Investigation of specific kinase-mediated effects - Specific and flexible pharmacologic intervention allows target validation of compounds from drug screens - Identification of direct substrates • Structure-based interpretation of the Jak mutations - Mutations within the FERM and SH2 domains - Mutations within the kinase-like domain - Mutations within the kinase domain • Perspectives Gain-of-function mutations in the genes encoding Janus kinases have been discovered in various haematologic diseases. Jaks are composed of a FERM domain, an SH2 domain, a pseudokinase domain and a kinase domain, and a complex interplay of the Jak domains is involved in regulation of catalytic activity and association to cytokine receptors. Most activating mutations are found in the pseudokinase domain. Here we present recently discovered mutations in the context of our structural models of the respective domains. We describe two structural hotspots in the pseudokinase domain of Jak2 that seem to be associated either to myeloproliferation or to lymphoblastic leukaemia, pointing at the involvement of distinct signalling complexes in these disease settings. The different domains of Jaks are discussed as potential drug targets. We present currently available inhibitors targeting Jaks and indicate structural differences in the kinase domains of the different Jaks that may be exploited in the development of specific inhibitors. Moreover, we discuss recent chemical genetic approaches which can be applied to Jaks to better understand the role of these kinases in their biological settings and as drug targets. [ABSTRACT FROM AUTHOR]