Cell lysates were prepared using immunoprecipitation compatible lysis buffer (20 mM Tris; pH 7

Cell lysates were prepared using immunoprecipitation compatible lysis buffer (20 mM Tris; pH 7. 4), 10 mM EDTA, 100 mM SGI-7079 NaCl, 1% polyethoxyethanol, 1 mM Na3VO4, 50 mM NaF, and protease inhibitor cocktail. Syk deficiency to enhance IFN and IL-10 in Syk deficient cells, confirmed by the overexpression of Akt (Myr-Akt) or constitutively active GSK3 (GSK3 S9A). Moreover, neither inhibition of PI3K-Akt signaling nor neutralization ofde novosynthesized IFN could rescue TNF and IL-6 production in LPS-stimulated Syk deficient cells. Syk deficiency resulted in decreased phosphorylation of IKK and the NF-B p65 subunit, further suggesting a SGI-7079 divergent influence of Syk of pro- and anti-inflammatory TLR responses. == Conclusions == Syk negatively regulates TLR4-mediated production of IFN and IL-10 and promotes inflammatory responses in dendritic cells through divergent regulation of downstream PI3K-Akt and NF-B signaling pathways. == General Significance == Syk DFNA23 may represent a novel target for manipulating the direction or intensity of the innate response, depending on clinical necessity. Keywords: Syk, Toll like receptor 4, Interferon beta, IL-10, PI3K, GSK3 == Introduction == Toll-like receptor (TLR)-mediated production of inflammatory cytokines and type I interferon (IFN) plays a critical role in the host response to microbial pathogens. Inflammatory cytokines promote the control of infection by elevating body temperature, activating and recruiting innate cells, enhancing phagocytosis, and boosting the adaptive arm of the immune system. Type I IFNs are particularly important in the control of viruses and cancers [13]. However , in order to prevent collateral tissue damage during inflammatory responses, the magnitude and quality of inflammatory cytokines and type I IFN must be tightly controlled [46]. TLR4-engagement results in the propagation of signals that will induce both inflammatory cytokines and type I IFNs in a manner mediated by the recruitment of different adaptor molecules. Whereas activation of TIRAP-MyD88 controls the induction SGI-7079 of pro- and anti- inflammatory cytokines through downstream NF-B-mediated transcription[7], the TRAM-TRIF-mediated signaling cascade controls the production of type I IFN, including IFN, SGI-7079 through two noncanonical IB kinases, TBK-1 and IKK, as well as NF-B, ATF-2/c-Jun, and IRF-3[810]. However , the regulatory signaling events involved in the control of TLR4-mediated inflammatory cytokines and type I IFN remain less well defined. Stimulation of TLR4 has been demonstrated to activate the PI3K pathway and restrain the production of pro-inflammatory cytokines through downstream phospho-inactivation of GSK3 in innate cells [11]. Our previous studies have identified the pivotal role of GSK3 in negative regulation of SGI-7079 TLR4-mediated IFN and IL-10 release [12, 13]. Cao et al. demonstrated that PI3K-mediated mTOR-p70S6K signaling is required for the induction of type I IFN production [14]. Since we have previously demonstrated that mTOR-p70S6K relays the TLR4-activated PI3K signal to the downstream GSK3 in innate immune cells [15], we hypothesized that PI3K-mTOR-p70S6K-GSK3 may be a major pathway responsible for regulation of IFN. Although above studies established the influence of PI3K on TLR-mediated inflammatory cytokine and IFN production, the molecular events upstream of the PI3K responsible for regulation of IFN and inflammatory cytokine production are still poorly understood. Spleen tyrosine kinase (Syk) is a 72kDa non-receptor tyrosine kinase primarily expressed by haematopoietic cells and typically considered as a crucial regulator in adaptive immunity. Syk deficiency leads to a complete absence of mature B cells and to severe defects in T cell development [1618]. Recent studies suggest that Syk may also be important in pattern recognition receptor (PRR)-mediated signaling in innate cells [1921]. Binding of the SH2 domain of Syk to phosphorylated immunoreceptor tyrosine-based activation motifs (ITAMs) of various PRRs and adaptors, such as C-type lectin receptors and DAP12 (DNAX activation protein of 12 kDa), enables Syk to relay the upstream signals initiated by these receptors [2224]. While the interaction of Syk with multiple ITAMs including MyD88, TRIF and TRAF6, is well established, the consequences of such interactions remain unclear. In this regard, using pharmacological inhibitors of Syk, several studies reported Syk is essential for TLR-mediated inflammatory responses, and inhibition of Syk suppresses the production of inflammatory mediators, including pro-inflammatory cytokines and IFN [2527]. In contrast, Syk was also reported to be involved in the CD11b-mediated inhibition of TLR signaling, by which it suppresses TLR-mediated pro-inflammatory cytokines and IFN [28]. These studies are further complicated by the finding of.