Yu Wakabayashi

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.

Cellular and molecular basis for the regulation of inflammation by TGF-β

Transforming growth factor-beta (TGF-beta) has been shown to play an essential role in the suppression of inflammation, yet recent studies have revealed the positive roles of TGF-beta in inflammatory responses. For example, TGF-beta induces Foxp3-positive regulatory T cells (iTregs) in the presence of interleukin-2 (IL-2), while in the presence of IL-6, it induces pathogenic IL-17 producing Th17 cells. TGF-beta inhibits the proliferation of immune cells as well as cytokine production via Foxp3-dependent and -independent mechanisms. Little is known about molecular mechanisms involved in immune suppression via TGF-beta; however, Smad2/3 have been shown to play essential roles in Foxp3 induction as well as in IL-2 and IFN-gamma suppression, whereas Th17 differentiation is promoted via the Smad-independent pathway. Interaction between TGF-beta and other cytokine signaling is important in establishing the balance of immunity and tolerance.

Smad2 and Smad3 Are Redundantly Essential for the TGF-β–Mediated Regulation of Regulatory T Plasticity and Th1 Development

Although it has been well established that TGF-β plays a pivotal role in immune regulation, the roles of its downstream transcription factors, Smad2 and Smad3, have not been fully clarified. Specifically, the function of Smad2 in the immune system has not been investigated because of the embryonic lethality of Smad2-deficient mice. In this study, we generated T cell-specific Smad2 conditional knockout (KO) mice and unexpectedly found that Smad2 and Smad3 were redundantly essential for TGF-β–mediated induction of Foxp3-expressing regulatory T cells and suppression of IFN-γ production in CD4+ T cells. Consistent with these observations, Smad2/Smad3-double KO mice, but not single KO mice, developed fatal inflammatory diseases with higher IFN-γ production and reduced Foxp3 expression in CD4+ T cells at the periphery. Although it has been suggested that Foxp3 induction might underlie TGF-β–mediated immunosuppression, TGF-β still can suppress Th1 cell development in Foxp3-deficient T cells, suggesting that the Smad2/3 pathway inhibits Th1 cell development with Foxp3-independent mechanisms. We also found that Th17 cell development was reduced in Smad-deficient CD4+ T cells because of higher production of Th17-inhibotory cytokines from these T cells. However, TGF-β–mediated induction of RORγt, a master regulator of Th17 cell, was independent of both Smad2 and Smad3, suggesting that TGF-β regulates Th17 development through Smad2/3-dependent and -independent mechanisms.

The mTOR pathway is highly activated in diabetic nephropathy and rapamycin has a strong therapeutic potential.

Diabetic nephropathy (DN) associated with type 2 diabetes is the most common cause of end-stage renal disease (ESRD) and a serious health issue in the world. Currently, molecular basis for DN has not been established and only limited clinical treatments are effective in abating the progression to ESRD associated with DN. Here we found that diabetic db/db mice which lack the leptin receptor signaling can be used as a model of ESRD associated with DN. We demonstrated that p70S6-kinase was highly activated in mesangial cells in diabetic obese db/db mice. Furthermore, systemic administration of rapamycin, a specific and potent inhibitor of mTOR, markedly ameliorated pathological changes and renal dysfunctions. Moreover, rapamycin treatment shows a significant reduction in fat deposits and attenuates hyperinsulinemia with few side effects. These results indicate that mTOR activation plays a pivotal role in the development of ESRD and that rapamycin could be an effective therapeutic agent for DN.

Gfi1 negatively regulates Th17 differentiation by inhibiting RORγt activity

T(h) cells have long been divided into two subsets, T(h)1 and T(h)2; however, recently, T(h)17 and inducible regulatory T (iTreg) cells were identified as new T(h) cell subsets. Although T(h)1- and T(h)2-polarizing cytokines have been shown to suppress T(h)17 and iTreg development, transcriptional regulation of T(h)17 and iTreg differentiation by cytokines remains to be clarified. In this study, we found that expression of the growth factor independent 1 (Gfi1) gene, which has been implicated in T(h)2 development, was repressed in T(h)17 and iTreg cells compared with T(h)1 and T(h)2 lineages. Gfi1 expression was enhanced by the IFN-gamma/STAT1 and IL-4/STAT6 pathways, whereas it was repressed by the transforming growth factor-beta1 stimulation at the promoter level. Over-expression of Gfi1 strongly reduced IL-17A transcription in the EL4 T cell line, as well as in primary T cells. This was due to the blockade of recruitment of retinoid-related orphan receptor gammat to the IL-17A promoter. In contrast, IL-17A expression was significantly enhanced in Gfi1-deficient T cells under T(h)17-promoting differentiation conditions as compared with wild-type T cells. In contrast, the impacts of Gfi1 in iTregs were not as strong as in T(h)17 cells. Taken together, these data strongly suggest that Gfi1 is a negative regulator of T(h)17 differentiation, which represents a novel mechanism for the regulation of T(h)17 development by cytokines.

SOCS3 in T and NKT Cells Negatively Regulates Cytokine Production and Ameliorates ConA-Induced Hepatitis

Suppressor of cytokine signaling 3 (SOCS3), a negative-feedback molecule for cytokine signaling, has been implicated in protection against liver injury. Previous studies have shown that overexpression of SOCS3 in the liver by adenovirus or membrane permeable recombinant protein protected the liver from various injuries. However it remained uncertain in which type of cells SOCS3 suppresses liver injury. In this study, we demonstrated that forced expression of SOCS3 in T and NKT cells suppressed ConA-induced hepatitis using T and NKT cell-specific SOCS3 transgenic (Lck-SOCS3 Tg) mice. IFN-γ and IL-4 production was reduced in Lck-SOCS3 Tg mice as well as splenocytes treated with ConA. IFN-γ and IL-4 levels were also reduced in Lck-SOCS3 Tg mice administrated with α-galactosylceramide, suggesting that SOCS3 in NKT cells has suppressive function. Sustained expression of SOCS3 in an NKT cell line also resulted in reduced expression of various cytokines and transcription factors. In contrast, T and NKT cell-specific SOCS3 conditional knockout (Lck-SOCS3 cKO) mice were hypersensitive to ConA-mediated hepatitis. Isolated SOCS3-deficient NKT cells produced higher levels of IFN-γ and IL-4. These data indicate that SOCS3 plays a negative regulatory role in NKT cell activation and that forced expression of SOCS3 in NKT cells is effective in preventing hepatitis.

Sprouty4 deficiency potentiates Ras-independent angiogenic signals and tumor growth

Sprouty proteins have been shown to negatively regulate a variety of receptor tyrosine kinase (RTK) signaling pathways and are considered to be tumor suppressor proteins. The pathophysiological functions of Sproutys in vivo remain to be investigated. In this study, we examined the physiological function of Sprouty4 as an angiogenic regulator, using Sprouty4 knockout (KO) mice and cells. We found that transplanted tumor cells grow much faster in Sprouty4 KO mice than in wild type (WT) mice, which we associate with enhanced neovascularization in the tumors transplanted into Sprouty4 KO mice. Moreover, vascular endothelial growth factor (VEGF)‐A‐induced angiogenesis and vascular permeability in vivo were enhanced in Sprouty4 KO mice compared with WT mice. Ex vivo angiogenesis, which we induced by VEGF‐A, basic fibroblast growth factor (bFGF), and sphingosine‐1‐phosphate (S1P), was also enhanced in the aortas of Sprouty4 KO mice. We demonstrated that Sprouty4 suppresses Ras‐independent VEGF‐A and S1P signaling, while it does not affect Ras‐dependent VEGF‐C signaling. These data indicate that Sprouty4 selectively suppresses Ras‐independent angiogenic factor signals and is an important negative regulator of pathophysiological angiogenesis. (Cancer Sci 2009; 100: 1648–1654)

Smad2 and Smad3 are redundantly essential for the suppression of iNOS synthesis in macrophages by regulating IRF3 and STAT1 pathways

Although transforming growth factor (TGF)-β1 is a well-known immunosuppressive cytokine, little is known about the role of its downstream transcription factors, Smad2 and Smad3, in the suppression of macrophage activation. Previous studies have demonstrated that Smad3 is critical for the suppression of LPS-mediated inducible nitric oxide (NO) synthase (iNOS) induction, although the role of Smad2 remains to be investigated. In this study, we found that iNOS induction was enhanced in Smad2-deficient bone marrow-derived macrophages (BMDMs) and peritoneal macrophages in vitro and tumor-associated macrophages in vivo, compared with wild-type (WT) macrophages. However, TGF-β1 still suppressed iNOS induction in Smad2-deficient macrophages. In Smad2/3 double knockout (KO) (Smad2/3 DKO) BMDMs, LPS-mediated NO/iNOS induction was more strongly elevated than in Smad2 or Smad3 single KO BMDMs, and its suppression by exogenous TGF-β1 was severely impaired. These data suggest that Smad2 and Smad3 redundantly regulate iNOS induction. Similarly, the production of IL-6 and TNFα, but not IL-10 was augmented in Smad2/3 DKO BMDMs, suggesting that Smad2 and Smad3 also redundantly suppressed some cytokines production. In Smad2/3 DKO macrophages, TLR3- as well as TLR4-mediated IRF3 activation and IFN-β production were strongly augmented, which resulted in hyper STAT1 phosphorylation. Furthermore, IFN-β- and IFN-γ-induced iNOS induction in the absence of TLR signaling and STAT1 transcriptional activity were augmented in Smad2/3 DKO BMDMs. These results suggest that Smad2 and Smad3 negatively regulate iNOS induction in macrophages by suppressing multiple steps in the IRF3-IFN-β-STAT1 pathway.

Histone 3 Lysine 9 (H3K9) Methyltransferase Recruitment to the Interleukin-2 (IL-2) Promoter Is a Mechanism of Suppression of IL-2 Transcription by the Transforming Growth Factor-β-Smad Pathway

Background: Suppression of IL-2 production from T cells is an important process for the immune regulation by transforming growth factor-beta (TGF-β). Results: Smad2 and Smad3 were redundantly essential for IL-2 suppression and recruited histone H3K9 methyltransferase, Suv39h1 to the proximal region of the IL-2 promoter, thereby suppressing IL-2 transcription. Conclusion: Smad2/3 mediated histone H3K9 trimethylation of the IL-2 promoter is an important mechanism for the suppression of IL-2 transcription. Significance: Our finding will be useful to establish a novel therapy for autoimmune diseases and inflammatory diseases. Suppression of IL-2 βproduction from T cells is an important process for the immune regulation by TGF-β. However, the mechanism by which this suppression occurs remains to be established. Here, we demonstrate that Smad2 and Smad3, two major TGF-β-downstream transcription factors, are redundantly essential for TGF-β-mediated suppression of IL-2 production in CD4+ T cells using Smad2- and Smad3-deficient T cells. Both Smad2 and Smad3 were recruited into the proximal region of the IL-2 promoter in response to TGF-β. We then investigated the histone methylation status of the IL-2 promoter. Although both histone H3 lysine 9 (H3K9) and H3K27 trimethylation have been implicated in gene silencing, only H3K9 trimethylation was increased in the proximal region of the IL-2 promoter in a Smad2/3-dependent manner, whereas H3K27 trimethylation was not. The H3K9 methyltransferases Setdb1 and Suv39h1 bound to Smad3 and suppressed IL-2 promoter activity in collaboration with Smad3. Overexpression of Suv39h1 in 68-41 T cells strongly inhibited IL-2 production in response to T cell receptor stimulation irrespective of the presence or absence of TGF-β, whereas Setdb1 overexpression only slightly suppressed IL-2 production. Silencing of Suv39h1 by shRNA reverted the suppressive effect of TGF-β on IL-2 production. Furthermore, TGF-β induced Suv39h1 recruitment to the proximal region of the IL-2 promoter in wild type primary T cells; however, this was not observed in Smad2−/−Smad3+/− T cells. Thus, we propose that Smads recruit H3K9 methyltransferases Suv39h1 to the IL-2 promoter, thereby inducing suppressive histone methylation and inhibiting T cell receptor-mediated IL-2 transcription.