Takatoshi Chinen

IL-6 induces an anti-inflammatory response in the absence of SOCS3 in macrophages

Whereas interleukin-6 (IL-6) is a proinflammatory cytokine, IL-10 is an anti-inflammatory cytokine. Although signal transducer and activator of transcription 3 (STAT3) is essential for the function of both IL-6 and IL-10, it is unclear how these two cytokines have such opposing functions. Here we show that suppressor of cytokine signaling 3 (SOCS3) is a key regulator of the divergent action of these two cytokines. In macrophages lacking the Socs3 gene or carrying a mutation of the SOCS3-binding site in gp130, the lipopolysaccharide-induced production of tumor necrosis factor (TNF) and IL-12 is suppressed by both IL-10 and IL-6. SOCS3 specifically prevents activation of STAT3 by IL-6 but not IL-10. Taken together, these data indicate that SOCS3 selectively blocks signaling by IL-6, thereby preventing its ability to inhibit LPS signaling.

Foxp3 Inhibits RORγt-mediated IL-17A mRNA Transcription through Direct Interaction with RORγt

The cytokine, transforming growth factor-β1 (TGF-β1), converts naive T cells into regulatory T cells that prevent autoimmunity. However, in the presence of interleukin (IL)-6, TGF-β1 has also been found to promote differentiation into IL-17-producing helper T (Th17) cells that are deeply involved in autoimmunity and inflammation. However, it has not been clarified how TGF-β1 and IL-6 determine such a distinct fate. Here we found that a master regulator for Th17, retinoic acid-related orphan receptor γt (RORγt), was rapidly induced by TGF-β1 regardless of the presence of IL-6. IL-6 reduced Foxp3 expression, and overexpression of Foxp3 in a T cell line resulted in a strong reduction of IL-17A expression. We have characterized the IL-17A promoter and found that RORγt binding is sufficient for activation of the minimum promoter in the HEK 293T cells. RORγt-mediated IL-17A promoter activation was suppressed by forced expression of Foxp3. Foxp3 directly interacted with RORγt through exon 2 region of Foxp3. The exon 2 region and forkhead (FKH) domain of Foxp3 were necessary for the suppression of RORγt-mediated IL-17A promoter activation. We propose that induction of Foxp3 is the mechanism for the suppression of Th17 and polarization into inducible Treg.

IFNγ-dependent, spontaneous development of colorectal carcinomas in SOCS1-deficient mice

Approximately 20% of human cancers are estimated to develop from chronic inflammation. Recently, the NF-κB pathway was shown to play an essential role in promoting inflammation-associated cancer, but the role of the JAK/STAT pathway, another important signaling pathway of proinflammatory cytokines, remains to be investigated. Suppressor of cytokine signaling-1 (SOCS1) acts as an important physiological regulator of cytokine responses, and silencing of the SOCS1 gene by DNA methylation has been found in several human cancers. Here, we demonstrated that SOCS1-deficient mice (SOCS1−/−Tg mice), in which SOCS1 expression was restored in T and B cells on a SOCS1−/− background, spontaneously developed colorectal carcinomas carrying nuclear β-catenin accumulation and p53 mutations at 6 months of age. However, interferon (IFN)γ−/−SOCS1−/− mice and SOCS1−/−Tg mice treated with anti-IFNγ antibody did not develop such tumors. STAT3 and NF-κB activation was evident in SOCS1−/−Tg mice, but these were not sufficient for tumor development because these are also activated in IFNγ−/−SOCS1−/− mice. However, colons of SOCS1−/−Tg mice, but not IFNγ−/−SOCS1−/− mice, showed hyperactivation of STAT1, which resulted in the induction of carcinogenesis-related enzymes, cyclooxygenase-2 and inducible nitric oxide synthase. These data strongly suggest that SOCS1 is a unique antioncogene which prevents chronic inflammation-mediated carcinogenesis by regulation of the IFNγ/STAT1 pathways.

SOCS1 is essential for regulatory T cell functions by preventing loss of Foxp3 expression as well as IFN-γ and IL-17A production

SOCS1 is required to restrict IFN-γ and IL-17 expression and maintain Foxp3 expression in and function of regulatory T cells.

STAT6 Inhibits TGF-β1-mediated Foxp3 Induction through Direct Binding to the Foxp3 Promoter, Which Is Reverted by Retinoic Acid Receptor

It has been shown that transforming growth factor β1 (TGF-β1) is critical in the generation of CD4+CD25+Foxp3+-inducible regulatory T cells (iTregs) from naïve CD4+T cells. However, in contrast to natural Tregs, TGF-β1-induced iTregs rapidly lose both Foxp3 expression and suppression activity. We found that TGF-β1-induced Foxp3 levels were maintained by the addition of the anti-interleukin 4 (IL-4) antibody or by STAT6 gene deletion. Thus, IL-4 is an important suppressor of Foxp3 induction, and T helper 2 development is a major cause for the disappearance of iTreg during long culture. Using promoter analysis in EL4 cells and primary T cells, we identified a silencer region containing a STAT6 binding site. STAT6 binding to this site reduced TGF-β1-mediated Foxp3 promoter activation and chromatin modification. Retinoic acid has also been shown to suppress loss of Foxp3 induced by TGF-β1. Retinoic acid in the presence of TGF-β1 reduced STAT6 binding to the Foxp3 promoter and enhanced histone acetylation, thereby reverting the effect of IL-4. We propose that antagonistic agents for neutralizing IL-4 could be a novel strategy to facilitate inducible Treg cell generation and the promotion of tolerance in Th2-dominated diseases such as allergy.

Mucosal T Cells Bearing TCRγδ Play a Protective Role in Intestinal Inflammation

Intestinal intraepithelial lymphocytes (IEL) bearing TCRγδ represent a major T cell population in the murine intestine. However, the role of γδ IEL in inflammatory bowel diseases (IBD) remains controversial. In this study, we show that γδ IEL is an important protective T cell population against IBD. γδ T cell-deficient (Cδ−/−) mice developed spontaneous colitis with age and showed high susceptibility to Th1-type 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced colitis at a young age. Transfer of γδ IEL to Cδ−/− mice ameliorated TNBS-induced colitis, which correlated with decrease of IFN-γ and TNF-α production and an increase of TGF-β production by IEL. Furthermore, a high level of IL-15, which inhibits activation-induced cell death to terminate inflammation, was expressed more in intestinal epithelial cells (EC) from TNBS-treated Cδ−/− mice than in those from wild-type mice. EC from wild-type mice significantly suppressed the IFN-γ production of IEL from TNBS-treated Cδ−/− mice, whereas EC from TNBS-treated Cδ−/− mice did not. These data indicate that γδ IEL play important roles in controlling IBD by regulating mucosal T cell activation cooperated with EC function. Our study suggests that enhancement of regulatory γδ T cell activity is a possible new cell therapy for colitis.

Selective expansion of foxp3-positive regulatory T cells and immunosuppression by suppressors of cytokine signaling 3-deficient dendritic cells.

Dendritic cells (DCs) induce immunity and immunological tolerance as APCs. It has been shown that DCs secreting IL-10 induce IL-10+ Tr1-type regulatory T (Treg) cells, whereas Foxp3-positive Treg cells are expanded from naive CD4+ T cells by coculturing with mature DCs. However, the regulatory mechanism of expansion of Foxp3+ Treg cells by DCs has not been clarified. In this study, we demonstrated that suppressors of cytokine signaling (SOCS)-3-deficient DCs have a strong potential as Foxp3+ T cell-inducing tolerogenic DCs. SOCS3−/− DCs expressed lower levels of class II MHC, CD40, CD86, and IL-12 than wild-type (WT)-DCs both in vitro and in vivo, and showed constitutive activation of STAT3. Foxp3− effector T cells were predominantly expanded by the priming with WT-DCs, whereas Foxp3+ Treg cells were selectively expanded by SOCS3−/− DCs. Adoptive transfer of SOCS3−/− DCs reduced the severity of experimental autoimmune encephalomyelitis. Foxp3+ T cell expansion was blocked by anti-TGF-β Ab, and SOCS3−/− DCs produced higher levels of TGF-β than WT-DCs, suggesting that TGF-β plays an essential role in the expansion of Foxp3+ Treg cells. These results indicate an important role of SOCS3 in determining on immunity or tolerance by DCs.

An essential role for the IL-2 receptor in Treg cell function

Regulatory T cells (Treg cells), which have abundant expression of the interleukin 2 receptor (IL-2R), are reliant on IL-2 produced by activated T cells. This feature indicates a key role for a simple network based on the consumption of IL-2 by Treg cells in their suppressor function. However, congenital deficiency in IL-2R results in reduced expression of the Treg cell lineage–specification factor Foxp3, which has confounded experimental efforts to understand the role of IL-2R expression and signaling in the suppressor function of Treg cells. Using genetic gain- and loss-of-function approaches, we found that capture of IL-2 was dispensable for the control of CD4+ T cells but was important for limiting the activation of CD8+ T cells, and that IL-2R-dependent activation of the transcription factor STAT5 had an essential role in the suppressor function of Treg cells separable from signaling via the T cell antigen receptor.

Suppressor of cytokine signaling-1 ameliorates dextran sulfate sodium-induced colitis in mice

Inflammatory bowel disease (IBD) is a chronic disorder of the gastrointestinal tract. Although the etiology and pathogenesis of IBD remain unknown, pro-inflammatory cytokines including IFN-gamma play an important role in the development of IBD. Suppressor of cytokine signaling-1 (SOCS-1) is a crucial inhibitor of cytokine signaling, particularly of IFN-gamma. In this study, we investigated the role of SOCS-1 in the development of murine dextran sulfate sodium (DSS)-induced colitis, a model of colitis resembling human IBD. SOCS-1 heterozygous (SOCS-1(+/-)) and wild-type (WT) mice were given 3% DSS dissolved in drinking water for 5 days. Activation and expression of signal transducers and activators of transcription (STAT) in colonic tissues were assessed by western blot analysis. The expression of CD4, IFN-gamma, IL-4, IL-17 and Forkhead box P3 (Foxp3) in colonic lamina propria lymphocytes was analyzed by flow cytometry and cytokine concentrations in serum were measured. DSS-treated SOCS-1(+/-) mice developed more severe colitis than DSS-treated WT mice. Enhanced activation of STAT1, a higher ratio of CD4(+)IFN-gamma(+) T cells and a lower frequency of Foxp3(+) regulatory T (Treg) cells, were observed in the colon of DSS-treated SOCS-1(+/-) mice compared with DSS-treated WT mice. DSS-treated SOCS-1(+/-) mice showed higher levels of IFN-gamma in sera than did DSS-treated WT mice. Furthermore, T cell-specific SOCS-1-conditional knockout mice developed more severe colitis than control mice after DSS administration. Our findings suggest that SOCS-1, particularly in T cells, prevents the development of DSS-induced colitis in mice by inhibiting IFN-gamma/STAT1 signaling and by subsequently regulating Treg cell development.

Prostaglandin E2 and SOCS1 have a role in intestinal immune tolerance

Interleukin 10 (IL-10) and regulatory T cells (Tregs) maintain tolerance to intestinal microorganisms. However, Il10−/−Rag2−/− mice, which lack IL-10 and Tregs, remain healthy, suggesting the existence of other mechanisms of tolerance. Here, we identify suppressor of cytokine signalling 1 (SOCS1) as an essential mediator of immune tolerance in the intestine. Socs1−/−Rag2−/− mice develop severe colitis, which can be prevented by the reduction of microbiota and the transfer of IL-10-sufficient Tregs. Additionally, we find an essential role for prostaglandin E2 (PGE2) in the maintenance of tolerance within the intestine in the absence of Tregs. Socs1−/− dendritic cells are resistant to PGE2-mediated immunosuppression because of dysregulated cytokine signalling. Thus, we propose that SOCS1 and PGE2, potentially interacting together, act as an alternative intestinal tolerance mechanism distinct from IL-10 and Tregs.