Kinase inhibition,competitive binding and proteasomal degradation: resolving the molecular function of the suppressor of cytokine signaling (SOCS) proteins

The suppressor of cytokine signaling (SOCS) family of proteins are key negative regulators of cytokine and growth factor signaling. They act at the receptor complex to modulate the intracellular signaling cascade, preventing excessive signaling and restoring homeostasis. This regulation is critical to the normal cessation of signaling, highlighted by the complex inflammatory phenotypes exhibited by mice deficient in SOCS1 or SOCS3. These two SOCS proteins remain the best characterized of the eight family members (CIS, SOCS1-7), and in particular, we now possess a sound understanding of the mechanism of action for SOCS3. Here, we review the mechanistic role of the SOCS proteins and identify examples where clear, definitive data have been generated and discuss areas where the information is less clear. From this functional viewpoint, we discuss how the SOCS proteins achieve exquisite and specific regulation of cytokine signaling and highlight outstanding questions regarding the function of the less well-studied SOCS family members.     

Regulation of innate immunity by suppressor of cytokine signaling (SOCS) proteins

Innate immunity represents the first line of defense against invading pathogens. Toll-like receptors (TLRs) are important for activation of innate immunity. Moreover, cytokines mediate communication of cells and are necessary to mount an appropriately regulated immune response. However, activation of innate immunity has to be tightly controlled to avoid overshooting immune reactions. Suppressor of cytokine signaling (SOCS) proteins have been identified as inducible feedback inhibitors of cytokine receptors and have been shown to be of crucial importance for the limitation of inflammatory responses. In this review, we describe the role of SOCS proteins in macrophages and dendritic cells (DCs). Based on our own findings, we show that SOCS proteins are directly induced by stimulation of TLRs. However, SOCS proteins do not interfere with direct TLR signaling, but avoid overshooting activation by regulating paracrine IFN-beta signaling. In addition, SOCS proteins in macrophages and DCs regulate the sensitivity towards IFN-gamma and GM-CSF, thereby modulating anti-microbial activity of macrophages and differentiation of DCs. We discuss that SOCS induction can also be used by microbes to evade immune defense, and this is exemplified by the parasite Toxoplasma gondii which induces SOCS1 to inhibit IFN-gamma-mediated macrophage activation. Taken together, the findings indicate that SOCS proteins play an important role in the balanced activation of innate immunity during infectious encounter.     

Regulation of multiple cytokine signalling pathways by SOCS3 is independent of SOCS2

Suppressor of cytokine signalling (SOCS) 3 is an essential regulator of cytokine signalling, and in turn its expression is tightly regulated. Data from overexpression studies in cell lines suggest that SOCS2 regulates SOCS3 protein degradation, by forming a molecular bridge to an E3 ubiquitin-ligase complex. Whether this regulation is relevant in primary cells is unknown. In this study, we utilized Socs2 ^{? / ?} mice to examine the role of SOCS2 in modulating SOCS3 expression and degradation, and its impact on interleukin-2 (IL-2) and IL-6 signalling in primary haemopoietic cells. Both biochemical and biological analyses demonstrated unperturbed SOCS3 expression and cytokine signalling in the absence of SOCS2. Our results suggest that SOCS2 is not a physiological regulator of SOCS3 expression and action in primary haemopoietic cells.     

Therapeutic hope for psoriasis offered by SOCS (suppressor of cytokine signaling) mimetic peptide

The cytokine network has a pivotal role in maintaining skin homeostasis, and the disturbance of this network can lead to skin pathogenesis. Evidence published in this issue of the European Journal of Immunology by Madonna et al. [Eur. J. Immunol. 2013. 43: 1883–1895], together with other recent data, focuses attention on a negative cytokine regulator, namely SOCS 1 (suppressor of cytokine signaling 1) in immune‐mediated skin disease. In addition, Madonna et al. bring new perspectives regarding the therapeutic control of IFN‐γ‐mediated skin pathogenesis by use of a SOCS 1 mimetic peptide.     

Inhibition of IL-6 family cytokines by SOCS3

IL-6 a multi-functional cytokine with important effects in both inflammation and haematopoiesis. SOCS3 is the primary inhibitor of IL-6 signalling, interacting with gp130, the common shared chain of the IL-6 family of cytokines, and JAK1, JAK2 and TYK2 to control both the duration of signalling and the biological response. Recent biochemical and structural studies have shown SOCS3 binds to only these three JAKs, all of which are associated with IL-6 signalling, and not JAK3. This specificity is determined by a three residue “GQM” motif in the kinase domain of JAK1, JAK2 and TYK2. SOCS3 binds to JAK and gp130 simultaneously, and inhibits JAK activity in an ATP-independent manner by partially occluding the kinase's substrate binding groove with its kinase inhibitory region. We therefore propose a model in which each of gp130, JAK and SOCS3 are directly bound to the other two, allowing SOCS3 to inhibit IL6 signalling with high potency and specificity.     

SOCS1基因沉默增强DC疫苗对肺癌动物模型的治疗效果

尽管树突状细胞(dendritic cell,DC)是机体内最有效的抗原提呈细胞(antigen presenting cell,APC),但由于逃逸机制的存在,基于DC的肿瘤疫苗效果并不如人意。因此,采用一定方法增强DC提呈抗原的能力是提高疫苗效能的关键。本研究中,采用RNA干扰技术(RNA interference,RNAi),沉默DC中细胞因子信号转导抑制因子1(suppressor of cyto- kine signaling 1,SOCS1)的表达,使之提呈抗原的能力显著提高,从而有效激发针对肿瘤的特异免疫应答,疫苗的治疗效果得以明显增强。     

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.     

Induction of suppressor of cytokine signaling-3 by herpes simplex virus type 1 confers efficient viral replication

We showed previously that infection of herpes simplex virus type 1 (HSV-1) rapidly induced the suppressor of cytokine signaling-3 (SOCS3), a host negative regulator of the JAK/STAT pathway, in the amnion cell line FL. Thus, HSV-1 suppresses the interferon (IFN) signaling pathway at the step of IFN-induced phosphorylation of janus kinases during an early infection stage. In the present study, we examined SOCS3 induction by HSV-1 infection in several types of human cell lines. FL cells and the T-cell line CCRF-CEM strongly induced SOCS3 during HSV-1 infection. The virus rapidly propagated in both cell lines and produced a lytic infection. On the other hand, the monocytic cell lines U937 and THP-1, and the B-cell line AKATA showed neither SOCS3 induction nor suppression of IFN-induced STAT1 phosphorylation during HSV-1 infection. These cell lines resulted in a persistent or prolonged infection, which continuously produced a low titer of infectious virus. The induction of SOCS3 by HSV-1 should occur via STAT3 activation immediately after HSV-1 infection. SOCS3 induction was inhibited by the addition of a Jak3 inhibitor WHI-P131. Treatment with WHI-P131 or transfection of antisense oligonucleotides specific for SOCS3 dramatically suppressed replication of HSV-1 in FL cells. The suppression of viral replication by WHI-P131 was released in the presence of neutralizing anti-IFN-alpha and anti-IFN-beta antibodies. In conclusion, suppression of IFN signaling by HSV-1-induced SOCS3 is required for efficient replication and lytic infection of HSV-1. The SOCS3 induction varied among cell lines, indicating that it is an important factor determining the cell type specificity of efficient HSV-1 replication.     

In situ detection of SOCS and cytokine expression in the uterine cervix from HIV/HPV coinfected women

The purpose of this study was to look for associations between a newly described class of suppressors of cytokine signaling (SSI/SOCS) and cytokine expression in the uterine cervix from HIV/HPV coinfected women. We examined the pro-inflammatory cytokines TNF-alpha and IL-6 since their expressions are linked and responsible for many aspects of both localized and systemic inflammatory responses. Further, expression of SSI/SOCS has been implicated in the negative feedback regulation of cytokine receptor signaling. PCR-amplified HIV-1 cDNA was noted mainly in the stroma, showing a perivascular distribution, and most of the infected cells colabeled with the macrophage marker CD68. The distribution of IL-6 and TNF-alpha was in the same area to HIV-1 and much greater than normal cervices from women with no evidence of viral infection. SOCS/SSI-1 and -3 mRNA positive cells in the uterine cervix were commonly detected in these noninfected cervical tissues; however, very few cells that contained SOCS were evident in areas where HIV-1, TNF-alpha, and IL-6 expressing cells were found. This suggests that viral-related suppression of SOCS/SSI-1-3 expression may be a factor in the marked local enhancement of TNF-alpha and IL-6 production which, in turn, may help facilitate viral spread; however, further studies should be done in order to elucidate the exact mechanisms of SOCS in the cervix.     

A regulatory role for suppressor of cytokine signaling-1 in T(h) polarization in vivo

Suppressor of cytokine signaling (SOCS)-1 is an inhibitory molecule for JAK, and its deficiency in mice leads to lymphocyte-dependent multi-organ disease and perinatal death. Crossing of SOCS-1(-/-) mice on an IFN-gamma(-/-), STAT1(-/-) and STAT6(-/-) background revealed that the fatal disease of SOCS-1(-/-) mice is also dependent on IFN-gamma/STAT1 and IL-4/STAT6 signaling pathways. Since IFN-gamma and IL-4 are representative T(h)1 and T(h)2 cytokines respectively, here we investigated the role of SOCS-1 in T(h) differentiation. Freshly isolated SOCS-1(-/-) CD4(+) T cells stimulated with anti-CD3 rapidly produced larger amounts of IFN-gamma and IL-4 than control cells, suggesting that these mutant T cells had already differentiated into T(h)1 and T(h)2 cells in vivo. In addition, SOCS-1(+/-) CD4(+) T cells cultured in vitro produced significantly larger amounts of IFN-gamma and IL-4 than SOCS-1(+/+) cells. Similarly, SOCS-1(+/-) CD4(+) T cells produced more IFN-gamma and IL-4 than SOCS-1(+/+) cells after infection with Listeria monocytogenes and Nippostrongyrus braziliensis respectively. Since IL-12-induced STAT4 and IL-4-induced STAT6 activation is sustained in SOCS-1(-/-) T cells, the enhanced T(h) functions in SOCS-1(-/-) and SOCS-1(+/-) mice appear to be due to the enhanced effects of these cytokines. These results suggest that SOCS-1 plays a regulatory role in both T(h)1 and T(h)2 polarizations.     

SOCS1对LIGHT诱导的骨髓来源DC分化成熟的影响

为探讨SOCS1是否参与LIGHT诱导的骨髓来源树突状细胞(BmDC)分化成熟,及其在此过程中的作用。RT-PCR检测受LIGHT刺激后小鼠BmDC、小鼠脾脏来源树突状细胞(sDC)中SOCS1mRNA水平及BmDCSOCS1mRNA水平的时间动力学;利用反义核苷酸技术抑制SOCS1的表达,通过流式细胞术(FACS)测定BmDC表面分子CD40、CD86的表达水平来分析阻断SOCS1对LIGHT诱导的BmDC分化成熟的影响。结果显示LIGHT刺激后,BmDCSOCS1mRNA水平迅速增高,并呈峰度变化,在4h时达到高峰;正常无SOCS1mRNA表达的sDC在加LIGHT后可检测到SOCS1mRNA;所设计SOCS1反义寡核苷酸能特异阻断SOCS1mRNA;在LIGHT作用下,SOCS1抑制组较非抑制组的CD40表达明显升高(P<0.05),CD86呈中度升高(P<0.05)。LIGHT在刺激BmDC分化成熟过程中上调了SOCS1的表达,阻断SOCS1使BmDC对LIGHT的反应更敏感,从而使BmDC成熟度更高;SOCS1对LIGHT诱导的BmDC分化成熟有负反馈调节作用。     

SOCS1/3对TLR3表达和T细胞分化的调控及其在桥本甲状腺炎中的作用

目的:探讨细胞信号传导抑制因子1/3(SOCS1、SOCS3,SOCS1/3)对Toll样受体3(TLR3)和T细胞分化的调控及其在桥本甲状腺炎(HT)中的作用。方法:收集已确诊的桥本甲状腺炎患者40例(HT组)及正常体检人群30例(对照组);通过Ficoll密度梯度离心法分离外周血单核细胞(PBMCs),流式细胞术检测调节性T细胞(CD4+CD25+Treg,Treg)、辅助性T细胞17(Th17)及滤泡辅助性T细胞(Tfh),免疫组化法(IHC)检测甲状腺组织中SOCS1/3及TLR3蛋白表达,ELISA检测血浆中SOCS1/3、STAT3蛋白水平,qRT-PCR检测PBMCs中TLR3、SOCS1/3、STAT3、RORγt、Bcl6、Foxp3 mRNA的表达水平。结果:HT组PBMCs中Treg细胞数量降低而Th17细胞、Tfh细胞数量升高(P <0. 05),TLR3、SOCS1/3、Bcl6、RORγt mRNA表达升高,Foxp3、STAT3 mRNA表达降低(P <0. 05); HT组甲状腺组织SOCS1/3蛋白、TLR3蛋白浓度升高(P <0. 05),STAT3蛋白表达降低(P <0. 05)。结论:HT患者SOCS1/3表达升高,可能对HT的TLR3表达及T细胞亚群分化起调控作用。     

Cortisol modulates the expression of cytokines and suppressors of cytokine signaling (SOCS) in rainbow trout hepatocytes

Although liver is a key target for corticosteroid action, its role in immune function is largely unknown. We tested the hypothesis that stress levels of cortisol down regulate immune-relevant genes in rainbow trout (Oncorhynchus mykiss) liver. Hepatocytes were treated with lipopolysaccharide (LPS) for 24h either in the presence or absence of cortisol. LPS stimulated heat shock protein 70 expression, enhanced glycolytic capacity, and reduced glucose output. LPS stimulated mRNA abundance of cytokines and serum amyloid protein A (SAA), while suppressors of cytokine signaling (SOCS)-3 was reduced. Cortisol increased mRNA abundances of IL-1β, SOCS-1 and SOCS-2, while inhibiting either basal or LPS-stimulated IL-8, TNF α2 and SAA. These cortisol-mediated effects were rescued by Mifepristone, a glucocorticoid receptor antagonist. Altogether, cortisol modulates the molecular immune response in trout hepatocytes. The upregulation of SOCS-1 and SOCS-2 by cortisol may be playing a key role in suppressing cytokine signaling and the associated inflammatory response.     

Runx1 promotes the development of glioma cells by regulating JAK-STAT signalling pathway

IntroductionHuman glioma is known as the most frequent and primary malignant tumour of the central nervous system with high aggression and poor prognosis. Runx1 is essential for haematopoiesis and is associated with tumour progression in several types of cancers. Therefore, this study aimed to investigate the effect and the possible regulatory mechanisms of Runx1 in glioma.Material and methodsThe expression of Runx1 in human glioma tissues was determined by qRT-PCR and immunohistochemistry (IHC). Subsequently, the effect of Runx1 on the glioma cell viability, migration, invasion and the protein level of p21, cyclin D1, MMP2, and MMP4 were detected by MTT, wound healing, transwell assays, and western blot, respectively, in U-138MG and U-251MG cell lines. We then explored the role of Runx1 in vivo by establishing a tumour-bearing mouse model.ResultsThe expression of Runx1 was significantly up-regulated in human glioma tissues and closely associated with tumour grade. Glioma patients with high Runx1 expression had decreased survival rate compared to those with low Runx1 level. Runx1 knockdown inhibited glioma cell viability, migration, invasion, and clone formation, while STAT3 suppressed these inhibitions. Moreover, Runx1 inhibited the activation of SOCS3/SOCS4 promoter, which in turn activated JAK/STAT3 signalling pathway. The tumour volume and weight of the siRunx1 group were lower than in the control group and the tumour mass grow more slowly as well.ConclusionsRunx1 promotes the development of glioma cells via JAK/STAT signalling pathway by inhibiting the activation of SOCS3/SOCS4 promoter.