STAT3 is a negative regulator of granulopoiesis but is not required for G-CSF-dependent differentiation

STAT3 has been described as an essential component of G-CSF-driven cell proliferation and granulopoiesis. This notion was tested by conditional gene ablation in transgenic mice. Contrary to expectation, granulocytes developed from STAT3 null bone marrow progenitors, and STAT3 null neutrophils displayed mature effector functions. Rather than a deficit in granulopoiesis, mice lacking STAT3 in their hematopoietic progenitors developed neutrophilia, and bone marrow cells were hyperresponsive to G-CSF stimulation. These studies provide direct evidence for STAT3-independent granulopoiesis and suggest that STAT3 directs a negative feedback loop necessary for controlling neutrophil numbers, possibly through induced expression of the signaling inhibitor, SOCS3.     

SOCS1/JAB is a negative regulator of LPS-induced macrophage activation

Bacterial lipopolysaccharide (LPS) triggers innate immune responses through Toll-like receptor (TLR) 4. We show here that the suppressor of cytokine-signaling-1 (SOCS1/JAB) is rapidly induced by LPS and negatively regulates LPS signaling. SOCS1(+/-) mice or SOCS1(-/-) mice with interferon-gamma (IFNgamma)-deficient background were more sensitive to LPS-induced lethal effects than were wild-type littermates. LPS-induced NO(2)(-) synthesis and TNFalpha production were augmented in SOCS1(-/-) macrophages. Furthermore, LPS tolerance, a protection mechanism against endotoxin shock, was also strikingly reduced in SOCS1(-/-) cells. LPS-induced I-kappaB and p38 phosphorylation was upregulated in SOCS1(-/-) macrophages, and forced expression of SOCS1 suppressed LPS-induced NF-kappaB activation. Thus, SOCS1 directly suppresses TLR4 signaling and modulates innate immunity.     

MUC1 mucin is a negative regulator of toll-like receptor signaling

MUC1 (MUC1 in humans and Muc1 in nonhuman species) is a transmembrane mucin-like glycoprotein expressed in epithelial cells lining various mucosal surfaces as well as hematopoietic cells. Recently, we showed that Muc1(-/-) mice exhibited greater inflammatory responses to Pseudomonas aeruginosa or its flagellin compared with their wild-type littermates, and our studies with cultured cells revealed that MUC1/Muc1 suppressed the Toll-like receptor (TLR) 5 signaling pathway, suggesting its anti-inflammatory role. Here we demonstrate that other TLR signaling (TLR2, 3, 4, 7, and 9) is also suppressed by MUC1/Muc1. The results from this study suggest that MUC1/Muc1 may play a crucial role during airway infection and inflammation by various pathogenic bacteria and viruses.     

Suppressor of cytokine signalling 1 (SOCS1) is a physiological regulator of the asthma response

Background The molecular determinants of the severity and persistence of allergic asthma remain poorly understood. Suppressor of cytokine signalling 1 (SOCS1) is a negative regulator of IL‐4‐dependent pathways in vitro and might therefore control T‐helper type 2 (Th2) immunity associated traits, such as IgE levels, mucin production, IL‐5 and IL‐13 induction, and eosinophilic mucosal inflammation, which are implicated in allergic asthma. Objective To investigate the role of SOCS1 in regulating Th2‐associated disease traits in a murine sub‐chronic aeroallergen‐driven asthma model. Methods Following sensitization and challenge with ovalbumin (OVA), bronchoalveolar lavage and serum were collected from mice lacking the Socs1 gene on an IFN‐γ null background (Socs1^?/?Ifnγ^?/?). The composition of infiltrating cells in the lung, serum IgE and IgG1 levels and cytokine levels were analysed. Results Serum IgE levels and infiltrating eosinophils were considerably increased in the lungs of OVA‐treated Socs1^?/?Ifnγ^?/? mice compared with Ifnγ^?/? and C57BL/6 controls. Expression of the Th2 cytokines, IL‐4, IL‐5 and IL‐13 was increased in CD4⁺ cells and lung tissue from OVA‐treated Socs1^?/?Ifnγ^?/? mice. IgE, IL‐5 levels and infiltrating eosinophils were also elevated in saline‐treated Socs1^?/?Ifnγ^?/? mice, suggesting that in the absence of SOCS1, mice are already biased towards a Th2 response. It is at present unclear whether the elevated cytokine levels are sufficient to result in the exacerbated Th2 response to OVA challenge or whether enhanced intra‐cellular signalling also contributes. Surprisingly, of the various IL‐4/IL‐13 responsive genes tested, only Arginase I appeared to be modestly up‐regulated in the lungs of OVA‐treated Socs1^?/?Ifnγ^?/? mice, suggesting that regulation by SOCS1 occurs primarily in haematopoietic cells and not in the airway epithelium. Conclusions Together these results indicate that SOCS1 is an important regulator of the Th2 response.     

PI3K is a negative regulator of IgE production

The production of IgE, a main player in allergic disorders such as asthma and atopic dermatitis, is strictly regulated and the serum concentrations of IgE are normally kept at a much lower level than other isotypes. We found that mice deficient for the p85alpha regulatory subunit of class IA phosphoinositide 3-kinase (PI3K) produced increasing amounts of serum IgE. Purified p85alpha-/- B cells produced more IgE than wild-type B cells in vitro in response to anti-CD40 mAb and IL-4. PI3K inhibitors wortmannin and IC87114 enhanced IgE production by wild-type B cells stimulated with anti-CD40 mAb and IL-4. Under the same condition, antigen receptor cross-linking induced the expression of inhibitor of differentiation-2 and suppressed the expression of activation-induced cytidine deaminase and class switch recombination (CSR) in a PI3K-dependent manner. IgE production was also suppressed in a concentrated cell culture condition, which was completely reversed by PI3K inhibition. The selective suppression of IgE production by PI3K was also observed at a protein level after CSR. Our results indicate that PI3K negatively regulates IgE production at both CSR and protein levels.     

Tulp3 is a critical repressor of mouse hedgehog signaling

Precise regulation of the morphogen sonic hedgehog (Shh) and modulation of the Shh signaling pathway is required for proper specification of cell fate within the developing limbs and neural tube, and resultant tissue morphogenesis. Tulp3 (tubby‐like protein 3) is a protein of unknown function which has been implicated in nervous system development through gene knockout studies. We demonstrate here that mice lacking the Tulp3 gene develop abnormalities of both the neural tube and limbs consistent with improper regulation of Shh signaling. Tulp3^?/? embryos show expansion of Shh target gene expression and display a ventralization of neural progenitor cells in the caudal neural tube. We further show that Tulp3^?/?/Shh^?/? compound mutant embryos resemble Tulp3 mutants, and express Shh target genes in the neural tube and limbs which are not expressed in Shh^?/? embryos. This work uncovers a novel role for Tulp3 as a negative regulatory factor in the Hh pathway. Developmental Dynamics 238:1140–1149, 2009. © 2009 Wiley‐Liss, Inc.     

TRAF1 is a negative regulator of TNF signaling. enhanced TNF signaling in TRAF1-deficient mice.

TNF receptor-associated factor 1 (TRAF1) is a unique TRAF protein because it lacks a RING finger domain and is predominantly expressed in activated lymphocytes. To elucidate the function of TRAF1, we generated TRAF1-deficient mice. TRAF1(-/-) mice are viable and have normal lymphocyte development. TRAF1(-/-) T cells exhibit stronger than wild-type (WT) T cell proliferation to anti-CD3 mAb, which persisted in the presence of IL-2 or anti-CD28 antibodies. Activated TRAF1(-/-) T cells, but not TRAF1(+/+) T cells, responded to TNF by proliferation and activation of the NF-kappa B and AP-1 signaling pathways. This TNF effect was mediated by TNFR2 (p75) but not by TNFR1 (p55). Furthermore, skin from TRAF1(-/-) mice was hypersensitive to TNF-induced necrosis. These findings suggest that TRAF1 is a negative regulator of TNF signaling.     

SIGIRR,a negative regulator of Toll-like receptor-interleukin 1 receptor signaling

The Toll-like receptor-interleukin 1 receptor signaling (TLR-IL-1R) receptor superfamily is important in differentially recognizing pathogen products and eliciting appropriate immune responses. These receptors alter gene expression, mainly through the activation of nuclear factor-kappaB and activating protein 1. SIGIRR (single immunoglobulin IL-1R-related molecule), a member of this family that does not activate these factors, instead negatively modulates immune responses. Inflammation is enhanced in SIGIRR-deficient mice, as shown by their enhanced chemokine induction after IL-1 injection and reduced threshold for lethal endotoxin challenge. Cells from SIGIRR-deficient mice showed enhanced activation in response to either IL-1 or certain Toll ligands. Finally, biochemical analysis indicated that SIGIRR binds to the TLR-IL-1R signaling components in a ligand-dependent way. Our data show that SIGIRR functions as a biologically important modulator of TLR-IL-1R signaling.     

Adiponectin is a negative regulator of antigen-activated T cells

Adiponectin (APN), a cytokine constitutively produced in fat tissue, has been shown to exert anti-inflammatory effects in various disease models. While the influence of APN on monocytic cells has been extensively studied in vitro, little is known about its role in T cells. In this study, we show that while <10% of human peripheral blood T cells express adiponectin receptors (AdipoRs) on their surface, most T cells store AdipoRs in intracellular compartments. AdipoRs colocalized with immune regulatory molecules CTLA-4 and TIRC7 within clathrin-coated vesicles. After stimulation, the expression of adiponectin receptor 1 (AdipoR1) and AdipoR2 was upregulated on the surface of antigen-specific T cells, as determined by tetramer or CD137 staining, and AdipoR1 and AdipoR2 coexpressed with CTLA-4. Addition of APN resulted in a significant diminution of antigen-specific T-cell expansion. Mechanistically, APN enhanced apoptosis and inhibited proliferation of antigen-specific T-cell lines. Further, APN directly inhibited cytokine production in response to antigen stimulation. In line with the in vitro data, APN-deficient (knockout, KO) mice had higher frequencies of CD137(+) T cells upon Coxsackie B virus infection. Altogether, our data suggest that APN is a novel negative T-cell regulator. In contrast to the CTLA-4 ligand B7 only expressed on APCs, APN is abundant in human plasma.     

Constitutively synthesized nitric oxide is a physiological negative regulator of mammalian angiogenesis mediated by basic fibroblast growth factor

We recently reported that the systemically administered nitric oxide synthase (NOS) inhibitor Nw-nitro-L-arginine methyl ester, L-NAME, administered before, during and after the angiogenic treatment stimulated angiogenesis induced by basic fibroblast growth factor, bFGF, in the rat. This suggests that suppression of constitutively expressed NOS, cNOS, plus inducible NOS, iNOS, and thus reduced production of nitric oxide, NO, was the stimulating factor. In those studies, the rat mesenteric-window angiogenesis assay was used. Moreover, the systemic administration of a NO releaser inhibited bFGF-mediated angiogenesis. Using the same experimental system, we have now studied whether the inhibition of cNOS alone in adult animals under physiological conditions, i.e. prior to the administration of the angiogenic stimulation with bFGF, affected the subsequent angiogenic response. cNOS constitute endothelial cell NOS (ecNOS) and neuronal NOS (nNOS). L-NAME or its inactive enantiomer Nw-nitro-D-arginine methyl ester, D-NAME, were given continuously in the drinking water (1.0 g/L) during 14 days prior to the start of the treatment with bFGF. The treatment with L-NAME significantly enhanced the subsequent angiogenic response. NO synthesized under physiological conditions by ecNOS in endothelial cells and platelets or nNOS in platelets may thus act as a first constitutional angiostatic factor in bFGF-mediated mammalian angiogenesis.     

SOCS3与BCR-ABL阴性的骨髓增殖性疾病

一系列细胞因子通过JAK/STAT通路诱导细胞因子信号转导抑制因子(SOCS)基因的表达,SOCS蛋白又负反馈调节细胞因子信号转导通路, 形成细胞因子信号转导反馈调节环。在BCR-ABL阴性的骨髓增殖性疾病的发病机制中,JAK2V617F点突变的发现是一个重大的突破。JAK2V617F点突变可导致SOCS3基因表达的增高,但通过某种机制逃逸了SOCS3的负向调控作用。     

Sulfated is a negative feedback regulator of wingless in Drosophila

Drosophila Wingless (Wg) acts as a morphogen to control pattern formation in a concentration dependent manner. Previous studies demonstrated important roles of heparan sulfate proteoglycans (HSPGs) in controlling Wg signaling and distribution. Here, we examined the role of Sulfated (Sulf1), a Drosophila homolog of vertebrate heparan sulfate 6‐O endosulfatase, in Wg signaling and distribution. We show that sulf1 is specifically up‐regulated by Wg signaling in the wing disc. We found that expression of Wg target gene senseless (sens) was elevated in the sulf1 mutant wing discs. Sulf1 also negatively regulate extracellular levels of Wg. Genetic interaction experiments indicate that Wg antagonist Notum may work synergistically with Sulf1 to restrict Wg signaling, and Dally, a member of Drosophila HSPGs, is a potential target of Sulf1. Our results demonstrate that sulf1 is a novel Wg target gene and by a feedback mechanism, it negatively regulated Wg signaling and distribution in vivo. Developmental Dynamics 240:640–648, 2011. © 2011 Wiley‐Liss, Inc.     

Tim-3, a negative regulator of anti-tumor immunity

T cell immunoglobulin-3 (Tim-3) was identified nearly 10 years ago as a negative regulator of IFN-γ-secreting CD4(+) T helper 1 and CD8(+) T cytotoxic 1 cells. Tim-3 is now classed with other inhibitory receptors, such as cytotoxic lymphocyte antigen-4 and programmed death-1 that are commonly referred to as immune checkpoint molecules. Recent studies have highlighted Tim-3 as an important player in the CD8(+) T cell exhaustion that takes place in chronic immune conditions such as chronic viral infection and cancer in both humans and experimental models. In addition to its role in exhausted T cells, recent data suggest that Tim-3 can further influence cancer outcome through its action on myeloid cells and cancer stem cells.