IL-27 suppresses CD28-mediated [correction of medicated] IL-2 production through suppressor of cytokine signaling 3

IL-27 is a novel IL-6/IL-12 family cytokine that not only plays a role in the early regulation of Th1 differentiation, but also exerts an inhibitory effect on immune responses, including the suppression of proinflammatory cytokine production. However, the molecular mechanism by which IL-27 exerts the inhibitory effect remains unclear. In this study we demonstrate that IL-27 inhibits CD28-mediated IL-2 production and that suppressor of cytokine signaling 3 (SOCS3) plays a critical role in the inhibitory effect. Although IL-27 enhanced IFN-gamma production from naive CD4+ T cells stimulated with plate-coated anti-CD3 and anti-CD28 in the presence of IL-12, IL-27 simultaneously inhibited CD28-mediated IL-2 production. Correlated with the inhibition, IL-27 was shown to augment SOCS3 expression. Analyses using various mice lacking a signaling molecule revealed that the inhibition of IL-2 production was dependent on STAT1, but not on STAT3, STAT4, and T-bet, and was highly correlated with the induction of SOCS3 expression. Similar inhibition of CD28-mediated IL-2 production and augmentation of SOCS3 expression by IL-27 were observed in a T cell hybridoma cell line, 2B4. Forced expression of antisense SOCS3 or dominant negative SOCS3 in the T cell line blocked the IL-27-inudced inhibition of CD28-mediated IL-2 production. Furthermore, pretreatment with IL-27 inhibited IL-2-mediated cell proliferation and STAT5 activation, although IL-27 hardly affected the induction level of CD25 expression. These results suggest that IL-27 inhibits CD28-mediated IL-2 production and also IL-2 responses, and that SOCS3, whose expression is induced by IL-27, plays a critical role in the inhibitory effect in a negative feedback mechanism.     

Inhibition of Kit expression by IL-4 and IL-10 in murine mast cells: role of STAT6 and phosphatidylinositol 3'-kinase.

The c-kit protooncogene encodes a receptor tyrosine kinase that is known to play a critical role in hemopoiesis and is essential for mast cell growth, differentiation, and cytokine production. Studies have shown that the Th2 cytokine IL-4 can down-regulate Kit expression on human and murine mast cells, but the mechanism of this down-regulation has remained unresolved. Using mouse bone marrow-derived mast cells, we demonstrate that IL-4-mediated Kit down-regulation requires STAT6 expression and phosphotidylinositide-3'-kinase activation. We also find that the Th2 cytokine IL-10 potently down-regulates Kit expression. IL-4 enhances IL-10-mediated inhibition in a manner that is STAT6 independent and phosphotidylinositide-3'-kinase dependent. Both IL-4- and IL-10-mediated Kit down-regulation were coupled with little or no change in c-kit mRNA levels, no significant change in Kit protein stability, but decreased total Kit protein expression. Inhibition of Kit expression by IL-4 and IL-10 resulted in a loss of Kit-mediated signaling, as evidenced by reduced IL-13 and TNF-alpha mRNA induction after stem cell factor stimulation. These data offer a role for STAT6 and phosphotidylinositide-3'-kinase in IL-4-mediated Kit down-regulation, coupled with the novel observation that IL-10 is a potent inhibitor of Kit expression and function. Regulating Kit expression and signaling may be essential to controlling mast cell-mediated inflammatory responses.     

Suppressor of cytokine signaling 1 inhibits IL-10-mediated immune responses

IL-10 has proved to be a key cytokine in regulating inflammatory responses by controlling the production and function of various other cytokines. The suppressor of cytokine signaling (SOCS) gene products are a family of cytoplasmic molecules that are essential mediators for negatively regulating cytokine signaling. It has been previously shown that IL-10 induced SOCS3 expression and that forced constitutive expression of SOCS3 inhibits IL-10/STAT3 activation and LPS-induced macrophage activation. In this report, we show that, in addition to SOCS3 expression, IL-10 induces SOCS1 up-regulation in all cell lines tested, including Ba/F3 pro-B cells, MC/9 mast cells, M1 leukemia cells, U3A human fibroblasts, and primary mouse CD4(+) T cells. Induction of SOCS molecules is dependent on STAT3 activation by IL-10R1. Cell lines constitutively overexpressing SOCS proteins demonstrated that SOCS1 and SOCS3, but not SOCS2, are able to partially inhibit IL-10-mediated STAT3 activation and proliferative responses. Pretreatment of M1 cells with IFN-gamma resulted in SOCS1 induction and a reduction of IL-10-mediated STAT3 activation and cell growth inhibition. IL-10-induced SOCS is associated with the inhibition of IFN-gamma signaling in various cell types, and this inhibition is independent of C-terminal serine residues of the IL-10R, previously shown to be required for other anti-inflammatory responses. Thus, the present results show that both SOCS1 and SOCS3 are induced by IL-10 and may be important inhibitors of both IL-10 and IFN-gamma signaling. IL-10-induced SOCS1 may directly inhibit IL-10 IFN-gamma signaling, while inhibition of other proinflammatory cytokine responses may use additional IL-10R1-mediated mechanisms.     

General nature of the STAT3-activated anti-inflammatory response

Although many cytokine receptors generate their signals via the STAT3 pathway, the IL-10R appears unique in promoting a potent anti-inflammatory response (AIR) via STAT3 to antagonize proinflammatory signals that activate the innate immune response. We found that heterologous cytokine receptor systems that activate STAT3 but are naturally refractory (the IL-22R), or engineered to be refractory (the IL-6, leptin, and erythropoietin receptors), to suppressor of cytokine signaling-3-mediated inhibition activate an AIR indistinguishable from IL-10. We conclude that the AIR is a generic cytokine signaling pathway dependent on STAT3 but not unique to the IL-10R.     

SOCS-1 protects against Chlamydia pneumoniae-induced lethal inflammation but hampers effective bacterial clearance

Suppressor of cytokine signaling 1 (SOCS1) plays a major role in the inhibition of STAT1-mediated responses. STAT1-dependent responses are critical for resistance against infection with Chlamydia pneumoniae. We studied the regulation of expression of SOCS1 and SOCS3, and the role of SOCS1 during infection with C. pneumoniae in mice. Bone marrow-derived macrophages (BMM) and dendritic cells in vitro or lungs in vivo all showed enhanced STAT1-dependent SOCS1 mRNA accumulation after infection with C. pneumoniae. Infection-increased SOCS1 mRNA levels were dependent on IFN-alphabeta but not on IFN-gamma. T or B cells were not required for SOCS1 mRNA accumulation in vivo. Infection-induced STAT1-phosphorylation occurred more rapidly in SOCS1(-/-) BMM. In agreement, expression of IFN-gamma responsive genes, but not IL-1beta, IL-6, or TNF-alpha were relatively increased in C. pneumoniae-infected SOCS1(-/-) BMM. Surprisingly, C. pneumoniae infection-induced IFN-alpha, IFN-beta, and IFN-gamma expression in BMM were attenuated by SOCS1. C. pneumoniae infection of RAG1(-/-)/SOCS1(-/-) mice induced a rapid lethal inflammation, accompanied by diminished pulmonary bacterial load and increased levels of iNOS and IDO but not IL-1beta, IL-6, or TNF-alpha mRNA. In summary, C. pneumoniae infection induces a STAT1, IFN-alphabeta-dependent and IFN-gamma independent SOCS1 mRNA accumulation. Presence of SOCS1 controls the infection-induced lethal inflammatory disease but impairs the bacterial control.     

Reprogramming of IL-10 activity and signaling by IFN-gamma

One important mechanism of cross-regulation by opposing cytokines is inhibition of signal transduction, including inhibition of Janus kinase-STAT signaling by suppressors of cytokine signaling. We investigated whether IFN-gamma, a major activator of macrophages, inhibited the activity of IL-10, an important deactivator. Preactivation of macrophages with IFN-gamma inhibited two key anti-inflammatory functions of IL-10, the suppression of cytokine production and of MHC class II expression. Gene expression profiling showed that IFN-gamma broadly suppressed the ability of IL-10 to induce or repress gene expression. Although IFN-gamma induced expression of suppressor of cytokine signaling proteins, IL-10 signal transduction was not suppressed and IL-10 activation of Janus kinases and Stat3 was preserved. Instead, IFN-gamma switched the balance of IL-10 STAT activation from Stat3 to Stat1, with concomitant activation of inflammatory gene expression. IL-10 activation of Stat1 required the simultaneous presence of IFN-gamma. These results demonstrate that IFN-gamma operates a switch that rapidly regulates STAT activation by IL-10 and alters macrophage responses to IL-10. Dynamic regulation of the activation of different STATs by the same cytokine provides a mechanism by which cells can integrate and balance signals delivered by opposing cytokines, and extends our understanding of cross-regulation by opposing cytokines to include reprogramming of signaling and alteration of function.     

TNF-alpha induces tyrosine phosphorylation and recruitment of the Src homology protein-tyrosine phosphatase 2 to the gp130 signal-transducing subunit of the IL-6 receptor complex

Recently, it has been demonstrated that TNF-alpha and LPS induce the expression of suppressor of cytokine signaling 3 (SOCS3) and inhibit IL-6-induced STAT3 activation in macrophages. Inhibitor studies suggested that both induction of SOCS3 and inhibition of IL-6-induced STAT3 activation depend on the activation of p38 mitogen-activated protein kinase. Since recruitment of the tyrosine phosphatase Src homology protein tyrosine phosphatase 2 (SHP2) to the signal-transducing receptor subunit gp130 attenuates IL-6-mediated STAT-activation, we were interested in whether TNF-alpha also induces the association of SHP2 to the gp130 receptor subunit. In this study we demonstrate that stimulation of macrophages and fibroblast cell lines with TNF-alpha causes the recruitment of SHP2 to the gp130 signal-transducing subunit and leads to tyrosine phosphorylation of SHP2 and gp130. In this context the cytoplasmic SHP2/SOCS3 recruitment site of gp130 tyrosine 759 is shown to be important for the inhibitory effects of TNF-alpha, since mutation of this residue completely restores IL-6-stimulated activation of STAT3 and, consequently, of a STAT3-dependent promoter. In this respect murine fibroblasts lacking exon 3 of SHP2 are not sensitive to TNF-alpha, indicating that functional SHP2 and its recruitment to gp130 are key events in inhibition of IL-6-dependent STAT activation by TNF-alpha. Furthermore, activation of p38 mitogen-activated protein kinase is shown to be essential for the inhibitory effect of TNF-alpha on IL-6 signaling and TNF-alpha-dependent recruitment of SHP2 to gp130.     

Loss of Kupffer cells in diet-induced obesity is associated with increased hepatic steatosis,STAT3 signaling,and further decreases in insulin signaling

While adipose tissue-associated macrophages contribute to development of chronic inflammation and insulin resistance of obesity, little is known about the role of hepatic Kupffer cells in this environment. Here we address the impact of Kupffer cell ablation using clodronate-encapsulated liposome depletion in a diet-induced obese (DIO) and insulin resistant mouse model. Hepatic expression of macrophage markers measured by realtime RT-PCR remained unaltered in DIO mice despite characteristic expansion of adipose tissue-associated macrophages. DIO mouse livers displayed increased expression of alternative activation markers but unaltered proinflammatory cytokine expression when compared to lean mice. Kupffer cell ablation reduced hepatic anti-inflammatory cytokine IL-10 mRNA expression in lean and DIO mice by 95% and 84%, respectively. Despite decreased hepatic IL-6 gene expression after ablation in lean and DIO mice, hepatic STAT3 phosphorylation, Socs3 and acute phase protein mRNA expression increased. Kupffer cell ablation in DIO mice resulted in additional hepatic triglyceride accumulation and a 30–40% reduction in hepatic insulin receptor autophosphorylation and Akt activation. Implicating systemic loss of IL-10, high-fat-fed IL-10 knockout mice also displayed increased hepatic STAT3 signaling and hepatic triglyceride accumulation. Insulin signaling was not altered, however. In conclusion, Kupffer cells are a major source of hepatic IL-10 expression, the loss of which is associated with increased STAT3-dependent signaling and steatosis. One or more additional factors appear to be required, however, for the Kupffer cell-dependent protective effect on insulin receptor signaling in DIO mice.     

IL-22-mediated liver cell regeneration is abrogated by SOCS-1/3 overexpression in vitro

The IL-10-like cytokine IL-22 is produced by activated T cells. In this study, we analyzed the role of this cytokine system in hepatic cells. Expression studies were performed by RT-PCR and quantitative PCR. Signal transduction was analyzed by Western blot experiments and ELISA. Cell proliferation was measured by MTS and [(3)H]thymidine incorporation assays. Hepatocyte regeneration was studied in in vitro restitution assays. Binding of IL-22 to its receptor complex expressed on human hepatic cells and primary human hepatocytes resulted in the activation of MAPKs, Akt, and STAT proteins. IL-22 stimulated cell proliferation and migration, which were both significantly inhibited by the phosphatidylinositol 3-kinase inhibitor wortmannin. IL-22 increased the mRNA expression of suppressor of cytokine signaling (SOCS)-3 and the proinflammatory cytokines IL-6, IL-8, and TNF-alpha. SOCS-1/3 overexpression abrogated IL-22-induced STAT activation and decreased IL-22-mediated liver cell regeneration. Hepatic IL-22 mRNA expression was detectable in different forms of human hepatitis, and hepatic IL-22 mRNA levels were increased in murine T cell-mediated hepatitis in vivo following cytomegalovirus infection, whereas no significant differences were seen in an in vivo model of ischemia-reperfusion injury. In conclusion, IL-22 promotes liver cell regeneration by increasing hepatic cell proliferation and hepatocyte migration through the activation of Akt and STAT signaling, which is abrogated by SOCS-1/3 overexpression.     

IL-10-independent STAT3 activation by Toxoplasma gondii mediates suppression of IL-12 and TNF-alpha in host macrophages

Infection of mouse macrophages by Toxoplasma gondii renders the cells resistant to proinflammatory effects of LPS triggering. In this study, we show that cell invasion is accompanied by rapid and sustained activation of host STAT3. Activation of STAT3 did not occur with soluble T. gondii extracts or heat-killed tachyzoites, demonstrating a requirement for live parasites. Parasite-induced STAT3 phosphorylation and suppression of LPS-triggered TNF-alpha and IL-12 was intact in IL-10-deficient macrophages, ruling out a role for this anti-inflammatory cytokine in the suppressive effects of T. gondii. Most importantly, Toxoplasma could not effectively suppress LPS-triggered TNF-alpha and IL-12 synthesis in STAT3-deficient macrophages. These results demonstrate that T. gondii exploits host STAT3 to prevent LPS-triggered IL-12 and TNF-alpha production, revealing for the first time a molecular mechanism underlying the parasite's suppressive effect on macrophage proinflammatory cytokine production.     

Cross Talk between the TM4SF5/Focal Adhesion Kinase and the Interleukin-6/STAT3 Pathways Promotes Immune Escape of Human Liver Cancer Cells

TM4SF5 overexpressed in hepatocellular carcinoma activates focal adhesion kinase (FAK) during tumor cell migration. However, it remains unknown how TM4SF5 in hepatocellular carcinoma cells compromises with immune actions initiated by extracellular cytokines. Normal and cancerous hepatocytes with or without TM4SF5 expression were analyzed for the effects of cytokine signaling activity on TM4SF5/FAK signaling and metastatic potential. We found that interleukin-6 (IL-6) was differentially expressed in hepatocytes depending on cancerous malignancy and TM4SF5 expression. IL-6 treatment activated FAK and STAT3 and enhanced focal adhesion (FA) formation in TM4SF5-null cells, but it decreased TM4SF5-dependent FAK activity and FA formation in SNU761-TM4SF5 cells. STAT3 suppression abolished the IL-6-mediated effects in normal Chang cells, but it did not recover the TM4SF5-dependent FAK activity that was inhibited by IL-6 treatment in cancerous SNU761-TM4SF5 cells. In addition, modulation of FAK activity did not change the IL-6-mediated STAT3 activity in either the Chang or SNU761 cell system. TM4SF5 expression in SNU761 cells caused invasive extracellular matrix degradation negatively depending on IL-6/IL-6 receptor (IL-6R) signaling. Thus, it is likely that hepatic cancer cells adopt TM4SF5-dependent FAK activation and metastatic potential by lowering IL-6 expression and avoiding its immunological action through the IL-6-STAT3 pathway.     

STAT3 is indispensable to IL-27-mediated cell proliferation but not to IL-27-induced Th1 differentiation and suppression of proinflammatory cytokine production

IL-27, a member of the IL-6/IL-12 family, activates both STAT1 and STAT3 through its receptor, which consists of WSX-1 and gp130 subunits, resulting in augmentation of Th1 differentiation and suppression of proinflammatory cytokine production. In the present study, we investigated the role of STAT3 in the IL-27-mediated immune functions. IL-27 induced phosphorylation of STAT1, -2, -3 and -5 in wild-type naive CD4+ T cells, but failed to induce that of STAT3 and STAT5 in STAT3-deficient cohorts. IL-27 induced not only proinflammatory responses including up-regulation of ICAM-1, T-box expressed in T cells, and IL-12Rbeta2 and Th1 differentiation, but also anti-inflammatory responses including suppression of proinflammatory cytokine production such as IL-2, IL-4, and IL-13 even in STAT3-deficient naive CD4+ T cells. In contrast, IL-27 augmented c-Myc and Pim-1 expression and induced cell proliferation in wild-type naive CD4+ T cells but not in STAT3-deficient cohorts. Moreover, IL-27 failed to activate STAT3, augment c-Myc and Pim-1 expression, and induce cell proliferation in pro-B BaF/3 transfectants expressing mutant gp130, in which the putative STAT3-binding four Tyr residues in the YXXQ motif of the cytoplasmic region was replaced by Phe. These results suggest that STAT3 is activated through gp130 by IL-27 and is indispensable to IL-27-mediated cell proliferation but not to IL-27-induced Th1 differentiation and suppression of proinflammatory cytokine production. Thus, IL-27 may be a cytokine, which activates both STAT1 and STAT3 through distinct receptor subunits, WSX-1 and gp130, respectively, to mediate its individual immune functions.     

Accelerated prion disease in the absence of interleukin-10

The identity of pro- and anti-inflammatory cytokines in the neuropathogenesis of prion diseases remains undefined. Here we have investigated the role of anti-inflammatory cytokines on the progression of prion disease through the use of mice that lack interleukin-4 (IL-4), IL-10, IL-13, or both IL-4 and IL-13. Collectively our data show that among these anti-inflammatory cytokines, IL-10 plays a prominent role in the regulation of prion disease. Mice deficient in IL-10 are highly susceptible to the development of prion disease and show a markedly shortened incubation time. In addition, we have correlated cytokine gene expression in prion-inoculated IL-10(-/-) mice to wild-type-inoculated animals. Our experiments show that in the absence of IL-10 there is an early expression of tumor necrosis factor alpha (TNF-alpha). In wild-type prion-inoculated mice, the expression of TNF-alpha mRNA occurs at a later time point that correlates with the extended incubation time for terminal disease development in these animals compared to those that lack IL-10. Elevated levels of IL-13 mRNA are found at early time points in the central nervous system of prion-inoculated IL-10(-/-) mice. At terminal disease, the brains of wild-type mice inoculated with RML or ME7 are characterized by elevated levels of mRNA for the proinflammatory cytokines TNF-alpha and IL-1beta, together with the anti-inflammatory cytokines IL-10, IL-13, and transforming growth factor beta. Our data are consistent with a role for proinflammatory cytokines in the initiation of pathology during prion disease and an attempt by anti-inflammatory cytokines to regulate the ensuing, invariably fatal pathology.     

The cytomegalovirus homolog of interleukin-10 requires phosphatidylinositol 3-kinase activity for inhibition of cytokine synthesis in monocytes

Human cytomegalovirus (CMV) has evolved numerous strategies for evading host immune defenses, including piracy of cellular cytokines. A viral homolog of interleukin-10, designated cmvIL-10, binds to the cellular IL-10 receptor and effects potent immune suppression. The signaling pathways employed by cmvIL-10 were investigated, and the classic IL-10R/JAK1/Stat3 pathway was found to be activated in monocytes. However, inhibition of JAK1 had little effect on cmvIL-10-mediated suppression of tumor necrosis factor alpha (TNF-alpha) production. Inhibition of the phosphatidylinositol 3-kinase/Akt pathway had a more significant impact on TNF-alpha levels but did not completely relieve the immune suppression, demonstrating that cmvIL-10 stimulates multiple signaling pathways to modulate cell function.