Email updates

Keep up to date with the latest news and content from Arthritis Research & Therapy and BioMed Central.

Highly Accessed Review

Negative regulation of cytokine signaling and immune responses by SOCS proteins

Akihiko Yoshimura*, Hitomi Nishinakamura, Yumiko Matsumura and Toshikatsu Hanada

Author affiliations

Division of Molecular and Cellular Immunology, Medical Institute of Bioregulation, Kyushu University, Fukuoka, Japan

For all author emails, please log on.

Citation and License

Arthritis Research & Therapy 2005, 7:100-110  doi:10.1186/ar1741

The electronic version of this article is the complete one and can be found online at:

Published:30 March 2005

© 2005 BioMed Central Ltd


Immune and inflammatory systems are controlled by multiple cytokines, including interleukins and interferons. Many of these cytokines exert their biological functions through JAKs (Janus tyrosine kinases) and STAT (signal transduction and activators of transcription) transcription factors. CIS (cytokine-inducible SH2 (Src homology 2) protein) and SOCS (suppressor of cytokine signaling) are a family of intracellular proteins, several of which have emerged as key physiological regulators of cytokine-mediated homeostasis, including innate and adaptive immunity. In this review we focus on the molecular mechanism of the action of CIS/SOCS family proteins and their roles in immune regulation and inflammatory diseases including rheumatoid arthritis.


Cytokines regulate many physiological responses and homeostasis, influencing the survival, proliferation, differentiation and functional activity of cells of the immune system, as well as those of most other organ systems [1]. Cytokines, including interleukins, IFNs and hemopoietins, activate the Janus kinases (JAK1, JAK2, JAK3 and Tyk2) that associate with their cognate receptors. Activated JAKs phosphorylate the receptor cytoplasmic domains that create docking sites for Src homology 2 (SH2)-containing signaling proteins. Among the substrates of tyrosine phosphorylation are members of the signal transducers and activators of transcription family of proteins (STATs) [2,3]. For example, IFN-γ uses JAK1 and JAK2, which activate mainly STAT1, whereas IL-6 binding to the IL-6 receptor α chain and gp130 activates primarily JAK1 and STAT3. Interestingly, the anti-inflammatory cytokine IL-10 also activates STAT3. STAT4 and STAT6 are essential for T helper (Th)1 and Th2 development, Because these are activated by IL-12 and IL-4, respectively. STAT5 is activated by many cytokines including IL-2, IL-7, erythropoietin and growth hormones. These are summarized in Fig. 1.

thumbnailFigure 1. The JAK/STAT (Janus family kinase/signal transduction and activators of transcription) pathway. EPO, erythropoietin; G-CSF, granulocyte colony-stimulating factor; IFN, interferon; IL, interleukin; JAK, Janus kinase; OSM, oncostatin M; STAT, signal transduction and activators of transcription; Th, T helper.

It has been recognized that sustained and/or excessive action of cytokines can be harmful to organisms. Accordingly, several mechanisms have been reported to modulate cytokine signaling to prevent this overaction of cytokines. For example, soluble forms of cytokine receptors that lack intracellular domains can inhibit the action of cytokines by simple competition for cytokine binding. Endocytosis of receptors and proteasomal degradation of signaling molecules after initial ligand stimulation is thought to have a role in preventing continuous cytokine signaling. In addition, several molecules that actively function as negative regulators of cytokine signaling, including SH2-containing phosphatase SHP-1, protein tyrosine phosphatase 1B (PTP1B), CD45 and T cell protein tyrosine phosphatase (TCPTP) [4] have also been reported to inhibit cytokine signaling as JAK phosphatases. The PIAS (protein inhibitors of activated STATs) family of proteins can inhibit the function of STATs by binding directly [5]. Moreover, recently accumulating evidence suggests that another family of proteins, suppressor of cytokine signaling (SOCS) proteins, is an important negative regulator for cytokine signaling [6,7].

CIS/SOCS family: structure and action mechanism

SOCS and cytokine-inducible SH2 protein (CIS) are a family of intracellular proteins, several of which have been shown to regulate the responses of immune cells to cytokines [6-10]. The discovery of the SOCS proteins seemed to have defined an important mechanism for the negative regulation of the cytokine–JAK–STAT pathway; however, recent studies using gene-disrupted (knockout; KO) mice have unexpectedly revealed profound roles of SOCS proteins in many immunological and pathological processes.

There are eight CIS/SOCS family proteins: CIS, SOCS1, SOCS2, SOCS3, SOCS4, SOCS5, SOCS6 and SOCS7; each has a central SH2 domain, an amino-terminal domain of variable length and sequence, and a carboxy-terminal 40-amino-acid module known as the SOCS box (Fig. 2). The SOCS box has also been found in ASBs (ankyrin repeat-containing proteins with a SOCS box), SSBs (SPRY domain-containing proteins with a SOCS box) and WSBs (WD40 repeat-containing proteins with a SOCS box), as well as other miscellaneous proteins. The SOCS-family members best characterized so far are CIS, SOCS1, SOCS2 and SOCS3.

thumbnailFigure 2. Structures of suppressor of cytokine signaling (SOCS) family molecules. CIS, Src homology 2 (SH2)-containing protein; EPO, erythropoietin; JAB, JAK (Janus family kinase)-binding protein; KIR, kinase inhibitory region; NAP4, Nck/Ash-binding protein 4; SSI-1, STAT (signal transducer and activator of transcription)-induced STAT inhibitor-1.

CIS was the first member identified in this family [11]. CIS and SOCS2 bind to phosphorylated tyrosine residues on activated (phosphorylated) cytokine receptors. Competition or steric hindrance for binding sites that are used to recruit and activate STATs (especially STAT5) has been proposed as the mechanism by which CIS and SOCS2 inhibit cytokine signaling [11,12]. CIS is induced by cytokines that activate STAT5 and bind to receptors that activate STAT5, namely erythropoietin, IL-2, IL-3, prolactin and growth hormone (GH) [11]. From an analysis of KO mice, SOCS2 has been shown to be a relatively specific negative regulator of GH–STAT5 [13,14]. SOCS5 has been shown to inhibit IL-4 signaling by interacting with the IL-4 receptor and inhibiting JAK1 binding to the receptor [15]. As mentioned below, receptor-CIS/SOCS complex is degraded by the ubiquitin–proteasome system, which could be an important inhibitory mechanism.

Both SOCS1 and SOCS3 can inhibit JAK tyrosine kinase activity because they have the kinase inhibitory region (KIR) in their N-terminal domain, which is proposed to function as a pseudosubstrate [16] (Fig. 3). A three-dimensional structural model of the SOCS1/JAK2 complex has been proposed [17]. Whereas SOCS1 binds directly to the activation loop of JAKs through its SH2 domain, the SOCS3 SH2 domain binds the cytokine receptor (Fig. 3). The SOCS3 SH2 domain has been shown to bind to Tyr757 of gp130, Tyr985 of the leptin receptor and Tyr401 of the erythropoietin receptor, Tyr729 of the granulocyte colony-stimulating factor (G-CSF) receptor, Tyr800 of the IL-12 receptor and Tyr985 of the leptin receptor, most being the same binding sites for protein tyrosine phosphatase 2 (SHP-2) [18-22]. De Souza and colleagues [23] have mapped the phosphopeptide binding preferences of the SH2 domain from SOCS3 by using degenerate phosphopeptide libraries. They found that the consensus ligand-binding motif for SOCS3 was pTyr-(Ser/Ala/Val/Tyr/Phe)-hydrophobic-(Val/Ile/Leu)-hydrophobic-(His/Val/Ile/Tyr). The sequence around Tyr759 of gp130 (-pTyr-Ser-Thr-Val-Val-His-) almost completely matches this motif. Although SOCS3 binds with a much higher affinity to a gp130 phosphopeptide around Tyr759 than to phospho-peptides derived from other receptors, such as leptin and erythropoietin receptors, multiple SOCS3-binding sites are predicted to exist in these receptors, which might compensate for weaker binding to individual sites.

thumbnailFigure 3. The molecular mechanism by which suppressor of cytokine signaling 1 (SOCS1) and SOCS3 negatively regulate Janus kinase (JAK) activation. SOCS1 binds to the JAKs and inhibits catalytic activity; SOCS3 binds to JAK-proximal sites on cytokine receptors and inhibits JAK activity through KIR (kinase inhibitory region). These complexes may be degraded by ubiquitination and proteasomal degradation recruited through the SOCS box.

The function of the SOCS box is the recruitment of the ubiquitin-transferase system. The SOCS box interacts with Elongins B and C, Cullin-5 or Cullin-2, Rbx-1 and E2 [24-26]. Thus, CIS/SOCS family proteins, as well as other SOCS-box-containing molecules, probably function as E3 ubiquitin ligases and mediate the degradation of proteins associated through their N-terminal regions. SOCS proteins therefore seem to combine specific inhibition (that is, kinase inhibition by KIR) and a generic mechanism of targeting interacting proteins for proteasomal degradation. The importance of the SOCS box has been recognized from the following evidence: the SOCS box of SOCS1 is necessary for the suppression of the oncogenic activity of TEL-JAK2 by SOCS1 [27,28] as well as for the degradation of wild-type activated JAK2 [29], and mice that were genetically modified to lack only the SOCS box of SOCS1 exhibited inflammatory diseases similar to complete SOCS1-deficient mice with slower onsets [30]. SOCS1 is also suggested to be involved in the degradation of Vav [31] and in the ubiquitination and degradation of a papilloma virus oncoprotein, E7 [32]. SOCS1 and SOCS3 have also been shown to downregulate insulin signaling by inducing the degradation of insulin receptor substrate (IRS)-1 and IRS-2 [33,34]. However, the SOCS box is also known to be important for stabilization and/or degradation of the SOCS1 and SOCS3 proteins themselves [24]. The role of the SOCS box in the function of each of the SOCS proteins remains to be investigated further.

Physiological function of CIS/SOCS molecules defined by gene targeting CIS1

CIS-transgenic mice exhibited growth retardation, impaired mammary gland development and reduced numbers of natural killer (NK) and NK T cells. These phenotypes in CIS-transgenic mice are remarkably similar to those observed in STAT5a KO and/or STAT5b KO mice [35], which is consistent with CIS having a specific role in the regulation of STAT5-mediated cytokine responses. Several reviews have mentioned that no obvious phenotype is observed in CIS KO mice but without showing any data. However, we have preliminary data suggesting that CIS is an important negative regulator of hematopoietic growth factors, including erythro-poietin, IL-3 and thrombopoietin (A Yoshimura, unpublished data). These are consistent with our initial proposal that CIS is a negative regulator of STAT5 [11].


Although SOCS1 KO mice are normal at birth, they exhibit stunted growth and die within 3 weeks with a syndrome characterized by severe lymphopenia, activation of peripheral T cells, fatty degeneration and necrosis of the liver, and macrophage infiltration of major organs (acute SOCS1-/- disease) [36,37]. The neonatal defects exhibited by SOCS1-/- mice seem to occur primarily as a result of unbridled IFN-γ signaling, because SOCS1-/- mice that also lack the IFN-γ gene or the IFN-γ receptor gene do not die neonatally [38-40]. Constitutive activation of STAT1 and constitutive expression of IFN-γ-inducible genes were observed in SOCS1 KO mice. These data strongly suggest that the excess IFN-γ is derived from the abnormally activated T cells in SOCS1-/- mice. However, SOCS1 also has important regulatory functions in IFN-γ-independent inflammatory diseases; these are discussed later.


SOCS2 is known to bind to GH receptors and to inhibit the activation of STAT5b induced by GH. SOCS2-deficient mice at 12 weeks after birth exhibited a 30 to 40% increase in body weight compared with control mice; they also showed hypertrophy of the liver and other visceral organs related to the increase in weight [14]. Growth promotion by GH is dependent on the induction of insulin-like growth factor-1 (IGF-1) by GH, whereas SOCS2-deficient mice do not exhibit an increase in serum IGF-1. Expression of SOCS2 is not directly induced by IGF-1 but is directly induced by GH. In SOCS2-deficient mice GH-induced STAT5 activation, but not IGF-1 signaling, is mildly enhanced [13]. Furthermore, SOCS2-/- STAT5b-/- double KO mice showed normal growth [13]. These data suggest that the action of SOCS2 is in the regulation of the GH signaling pathway.


SOCS3 KO mice die by placental function defects during the embryonic stage of development [41,42]. Deletion of SOCS3 causes an embryonic lethality that can be saved by a tetraploid rescue approach, which demonstrates an essential role in placental development and a non-essential role in embryo development. Rescued SOCS3-deficient mice show a prenatal lethality with cardiac hypertrophy, suggesting that SOCS3 is essential for regulating LIF receptors or gp130 signaling [42]. Conditional KO mice studies demonstrated that SOCS3 is an important negative regulator of IL-6 [43-45] and G-CSF [46,47]. Mice in which the SOCS3 gene was deleted in all hematopoietic cells developed neutrophilia and a spectrum of inflammatory pathologies [47]. When stimulated with G-CSF in vitro, SOCS3-deficient cells of the neutrophilic granulocyte lineage exhibited prolonged STAT3 activation and enhanced cellular responses to G-CSF [46,47]. SOCS3-deficient mice injected with G-CSF displayed enhanced neutrophilia, progenitor cell mobilization and splenomegaly, but unexpectedly also developed inflammatory neutrophil infiltration into multiple tissues and consequent hindleg paresis [47]. Interestingly, conditional STAT3 deletion in neutrophils also exhibited hyper-responses to G-CSF [48], suggesting that a major role of STAT3 in neutrophils is the induction of SOCS3. It is probable that the ERK (extracellular signal-related kinase) pathway induced by G-CSF has a major function in the proliferation and differentiation of neutrophils.

Recently, the essential roles of SOCS3 in endocrine systems have also been clarified. Administration of leptin to neural cell-specific SOCS3 conditional KO mice greatly reduces their food intake and causes enhanced body weight loss compared with wild-type mice, indicating that SOCS3 in the brain negatively regulates leptin signaling [49]. Similar findings were observed in SOCS3 heterozygous mice [50]. Moreover, Socs3-deficient mice were resistant to weight gain and hyperleptinemia induced by a high-fat diet, and sensitivity to insulin was retained. These data indicate that SOCS3 is a key regulator of diet-induced leptin and also insulin resistance [49]. In addition, SOCS3-deficient adipocytes generated from SOCS3 KO fibroblasts are significantly protected from tumor necrosis factor (TNF)-α-induced insulin resistance, mainly due to reduced proteasomal degradation of IRS proteins by TNF-α, suggesting that SOCS3 is an important mediator of insulin resistance in vivo [51]. Taken together, these results indicate that SOCS3 can be a potential therapeutic target for many prevalent human metabolic disorders such as obesity and diabetes.


A study with SOCS5 transgenic mice suggested that SOCS5 inhibits Th2 differentiation by inhibiting IL-4 signaling [14]. SOCS5 is expressed preferentially in Th1 cells and SOCS5 can interact with the IL-4 receptor in the absence of tyrosine phosphorylation. This interaction of SOCS5 with the IL-4 receptor is likely to cause the reduction in IL-4-induced activation of STAT6 and thus to regulate Th2 polarization. In line with this finding, T cells from SOCS5 transgenic mice also exhibit reduced Th2 polarization. However, a recent analysis of SOCS5 KO mice failed to confirm the roles of SOCS5 in lymphocyte function [52]. CD4+ T cells in SOCS5 KO mice showed a normal Th1/Th2 response both in vitro and in vivo. The conflicting findings in SOCS5 KO mice may be explained by SOCS5 being compensated for by other SOCS proteins such as SOCS4, because SOCS4 shares significant homology with SOCS5. Further analyses including those of SOCS4/SOCS5 double KO mice may be required to address the function of SOCS5 in vivo.

A Drosophila SOCS protein that is highly homologous to mammalian SOCS5 was cloned and named SOCS36E. Interestingly, ectopic expression of SOCS36E in transgenic flies results in phenotypes resembling those of flies defective in JAK/STAT or epidermal growth factor signaling [53]. This result could imply that mammalian SOCS5 is also involved in the regulation of JAK/STAT and/or epidermal growth factor signaling in mammals, but future studies are required to address this issue.


Mice lacking SOCS6 have been generated and develop normally with the exception of a 10% reduction in weight compared with wild-type littermates [54]. SOCS6 mRNA was expressed ubiquitously in murine tissues [54]. SOCS6 and SOCS7 SH2 domains interacted with a protein complex consisting of IRS-4, IRS-2 and the p85 regulatory subunit of phosphoinositide 3-kinase. However, there is no evidence so far to suggest that SOCS6 might be involved in the degradation of proteins [54].


SOCS7 is highly expressed in the brain. SOCS7-/- mice were 7 to 10% smaller than their wild-type littermates, and within 15 weeks of age about 50% of the SOCS7-deficient mice died as a result of hydrocephalus that was characterized by cranial distortion, dilation of the ventricular system, reduced thickness of the cerebral cortex and disorganization of the subcommissural organ [55]. Thus, SOCS7 is important in the functioning of neuronal cells.

SOCS1 and innate immunity

SOCS1 deficiency in the hematopoietic compartment is thought to be sufficient to cause a SOCS1-/- disease, because transfer of SOCS1-/- bone marrow into irradiated JAK3-deficient recipients results in premature lethality [38,56]. SOCS1-/- rag-2-/- mice do not die prematurely [38], and SOCS1-/- NK T cells have been reported to be more numerous than normal in the liver and to be cytotoxic for syngenic liver cells [57]. T and/or NK T cells have therefore been suggested to have essential functions in SOCS1-/- diseases. However, mice lacking the SOCS1 gene, specifically in T and NK T cells, did not develop any of the inflammatory pathologies or neonatal death found in SOCS1-/- mice [58]. This indicates that other hematopoietic cells in addition to T and NK T cells are deeply involved in SOCS1-/- inflammatory diseases. Strong candidates are antigen-presenting cells including macrophages and dendritic cells (DCs).

Bacterial lipopolysaccharide (LPS) triggers innate immune responses through Toll-like receptor 4 (TLR4). Other bacterial pathogens including proteoglycans and CpG-DNA also activate other TLR-family receptors. Regulation of TLR signaling is a key step in inflammation, septic shock and innate/adaptive immunity. SOCS1 and SOCS3 were found to be induced by LPS or CpG-DNA stimulation in macrophages [59-61]. SOCS1 has been implicated in hypo-responsiveness to cytokines such as IFN-γ after the exposure of macrophages to LPS [61]. Furthermore, SOCS1-deficient mice are found to be more sensitive to LPS shock than wild-type littermates [62,63]. SOCS1-/- mice (before disease onset), SOCS1+/- mice and IFN-γ-/- SOCS1-/- mice, as well as STAT1-/-SOCS1-/- mice, have all been shown to be hyper-responsive to LPS and very sensitive to LPS-induced lethality. Macrophages from these mice produced increased levels of the pro-inflammatory cytokines, such as TNF-α and IL-12, as well as nitric oxide (NO), in response to LPS. One important mechanism of the suppression of LPS-induced macrophage activation by SOCS1 is the inhibition of IFN-β signaling indirectly activated by LPS [64,65]. However, a direct effect of SOCS1 on the TLR-NF-κB pathway has been also proposed [62,63]. Ryo and colleagues [66] showed that direct binding of SOCS1 to the p65 subunit of NF-κB induces proteasomal degradation of p65, which is one potential mechanism of TLR signal suppression by SOCS. Moreover, LPS tolerance was severely impaired in SOCS1-/- mice and SOCS1-deficient peritoneal macrophages [62,63]. However, Gingras and colleagues [64] did not observe enhanced LPS responses in SOCS1-deficient bone marrow-derived macrophages cultured with macrophage colony-stimulating factor (M-CSF). The nature of bone marrow-derived macrophages cultured in M-CSF in vitro is different from that of primary peritoneal macrophages [62-64]. SOCS1-deficient macrophages in tissue may be already affected by various environmental cytokines. Even so, SOCS1 is still deeply involved in the regulation of macrophage activation through regulating not only the JAK/STAT pathway but also the TLR-NF-κB pathway (Fig. 4).

thumbnailFigure 4. Regulation of lipopolysaccharide (LPS) signaling by suppressor of cytokine signaling 1 (SOCS1). LPS stimulates NF-κB and the JNK/p38 pathway through Toll-like receptor (TLR)4/MD2 receptor. IFN-β is rapidly induced through the TRIF/IRF-3 pathway and activates the JAK/STAT1 (Janus kinase/signal transduction and activators of transcription 1) pathway. SOCS1 is probably induced by STAT1 and NF-κB, and then suppresses both STAT1 and NF-κB. One possible mechanism of NF-κB suppression is the induction of degradation of the p65 NF-κB subunit.

SOCS1-deficient DCs are also hyper-activated and may be involved in the pathology found in SOCS1-/- mice [67]. We generated mice in which SOCS1 expression was restored in T and B cells on a SOCS1-/- background (SOCS1-/-transgenic mice). In these mice, DCs were abnormally accumulated in the thymus and spleen and produced high levels of BAFF/BLyS and APRIL, resulting in the aberrant expansion of B cells and autoreactive antibody production. SOCS1-deficient DCs efficiently stimulated B cell proliferation in vitro and autoantibody production in vivo. These results indicate that SOCS1 is essential to normal DC functions and to the suppression of systemic autoimmunity that develops in SOCS1-/- transgenic mice [67]. Furthermore, we speculate that SOCS1-/- DCs are important in the onset of SOCS1-/- diseases, because SOCS1-deficient DCs can activate the proliferation not only of B cells but also of allogenic T cells [67]. We also observed that T cells produce higher amounts of Th1 cytokines such as IFN-γ and TNF-α in response to SOCS1-/- DCs than to wild-type DCs [68]. This nature of SOCS1-deficient DCs can be applied to anti-tumor immunity, because strong Th1 induction is believed to be important for DC-mediated vaccination. Shen and colleagues [69] reported that silencing the SOCS1 gene by using short-interfering-RNA (siRNA) technology in antigen-presenting DCs strongly enhances antigen-specific anti-tumor immunity. They showed that DCs transfected with SOCS1 siRNA were more responsive to LPS or IFN-γ than were DCs transfected with control siRNA, as indicated by an enhanced secretion of proinflammatory cytokines such as IL-6 and TNF-α and by the enhanced phosphorylation of STAT1, IκB and JNK upon stimulation. Antigen (ovalbumin) peptide-pulsed SOCS1-siRNA-treated DCs stimulated ovalbumin-specific cytotoxic T cell proliferation and functioned more strongly than did control DCs. These data indicate that SOCS1-deficient DCs can strongly activate CD4+ (helper) and CD8+ (cytotoxic) T cells.

SOCS3 and innate immunity

IL-6 is a pro-inflammatory cytokine that has a progressive function in many inflammatory diseases, whereas IL-10 is an immunoregulatory cytokine that has potent anti-inflammatory activity. Although the transcription factor STAT3 is essential for the function of both IL-6 and IL-10 [70], it is not clear how these two cytokines exhibit such opposite functions. Recently, we demonstrated that at least in macrophages 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 (Y759F) in gp130, not only IL-10 but also IL-6 suppressed LPS-induced TNF-α production [43]. SOCS3 protein was strongly induced by both IL-6 and IL-10 in the presence of LPS, but selectively inhibited IL-6 signaling, because SOCS3 bound the IL-6 receptor, gp130 (Y759), but not the IL-10 receptor [43]. These data indicate that SOCS3 selectively blocks IL-6 signaling, interfering with its ability to inhibit LPS signaling (Fig. 5). Consistent with this is the observation that mice specifically lacking the SOCS3 gene in macrophages and neutrophils are resistant to acute inflammation as modeled by LPS shock. This phenotype is the complete opposite to macrophages in STAT3 conditional KO mice, which are more sensitive to LPS shock and produce more TNF-α in response to LPS [70]. We also found a similar opposite relationship between STAT3 and SOCS3 on DC activation (Y Matsumura and A Yoshimura, unpublished data).

thumbnailFigure 5. Regulation of lipopolysaccharide (LPS) signaling by STAT3 (signal transduction and activators of transcription 3) and suppressor of cytokine signaling 3 (SOCS3) in macrophages. SOCS3 strongly suppresses STAT3 activated by IL-6/gp130 but not by IL-10, because SOCS3 does not bind to the IL-10 receptor. STAT3 is shown to suppress LPS signaling through STAT3, but the molecular mechanism of this process has not been clarified.

Others have shown that IL-6 strongly activates STAT1 and induces the expression of IFN-responsive genes in SOCS3-deficient macrophages, implying that IL-6 might mimic the action of IFNs [44,45]. Interestingly, these reports also demonstrated that the absence of SOCS3 in macrophages changes the original function of IL-6. All three studies therefore indicate that SOCS3 is an important regulator to maintain a specific biological function on gp130-related cytokines in vivo. From such an interesting biochemical and biological function of SOCS3, we might be able to convert inflammatory cytokine IL-6 to an anti-inflammatory cytokine by suppressing the expression of SOCS3 in macrophages.

SOCS1 and inflammatory diseases

Given the wide range of immunoregulatory functions, SOCS1 might be implicated in the pathology of inflammatory diseases. In a murine model of autoimmune arthritis, joint inflammation and destruction was significantly enhanced in mice lacking SOCS1 [71,72]. Blood CD4+ T cells from patients with rheumatoid arthritis (RA) contained higher levels of SOCS1 but lower levels of SOCS3 mRNA than control CD4+ T cells, as determined by real-time polymerase chain reaction [73]. This higher expression of SOCS1 in T cells might explain the imbalance of the Th1/Th2 response or the resistance of T cells to IL-10 found in RA patients. In contrast, zymosan-induced arthritis was ameliorated in IL-6-deficient mice but exacerbated in STAT1-deficient mice [74], indicating that STAT1 is involved in the suppression of inflammation in this model. In STAT1-/- mice, gene expression of synovial SOCS1, but not that of SOCS3, was markedly reduced in STAT1-deficient mice. The expression of SOCS1 could be the underlying mechanism by which STAT1 controls joint inflammation. The important role of SOCS1 in joint inflammation and arthritis will probably be defined by conditional gene knockout.

SOCS1 has so far been shown to be deeply involved in hepatitis in humans. We found that SOCS1 gene silencing by DNA methylation is frequently observed in hepatitis induced by HCV infection [75], and SOCS1 gene methylation was well correlated with the severity of liver fibrosis, suggesting that decreasing SOCS1 gene expression by DNA methylation promotes liver inflammation.

SOCS3 and inflammatory diseases

There is accumulating evidence that SOCS3 could suppress inflammatory reactions in pathological situations in which IL-6-related cytokines have important progressive functions. This is because SOCS3 is a relatively specific inhibitor of gp130 as described above. STAT3 activation and high SOCS3 expression levels have been found in epithelial and lamina propria cells in the colon of IBD (inflammatory bowel disease) model mice, as well as in human ulcerative colitis and patients with Crohn's disease [76], and in synovial fibroblasts of patients with RA [77]. In a dextran sulfate sodium-induced mouse colitis model, a time-course experiment indicated that STAT3 activation was 1 day ahead of SOCS3 induction; STAT3 activation became apparent during days 3 to 5 and decreased thereafter, whereas SOCS3 expression was induced at day 5 and maintained high levels thereafter. In murine models of inflammatory synovitis, STAT3 phosphorylation preceded SOCS3 expression, which is consistent with the idea that SOCS3 is part of the STAT3 negative-feedback loop [76]. We have shown that overexpression of SOCS3 by adenoviral gene transfer could prevent the development of experimental arthritis [77]. The IL-6/STAT3 pathway therefore promotes the progression of the chronic status of diseases by contributing to cytokine and growth factor production, tissue hyperplasia, synovial fibroblast proliferation, fibrosis and osteoclast activation. On the basis of the evidence that forced expression of SOCS3 can inhibit IL-6-mediated STAT3 activation, we propose that SOCS3 is a negative regulator of inflammatory diseases in synovial fibroblasts, especially in those in which IL-6 levels are very high. A mouse line of mutated gp130 in which the SHP-2/SOCS3-binding site was disrupted developed a RA-like joint disease with increased production of Th1-type cytokines and immunoglobulins of the IgG2a and IgG2b classes [78]. In another case, gastrointestinal inflammation and adenoma were observed in similar mutant mice [79]. SOCS3 is therefore also critical in the development of chronic inflammatory disease. These studies reinforce the idea that cytokines operating through gp130 are probably important in activating RA synovial fibroblasts. Modulation of the gp130–JAK–STAT pathway is therefore a reasonable strategy for the development of new anti-inflammatory drugs. Specific JAK kinase inhibitors might have a therapeutic role in treating this and other disorders of the immune system, especially if toxicity does not preclude their use.

In contrast, the enhanced action of SOCS3 may promote allergic responses, because a recent analysis indicated that transgenic SOCS3 expression in T cells inhibits Th1 development and promotes Th2 development [80]. Indeed, that report also describes that increased SOCS3 expression in T cells is correlated with the severity of human allergic diseases such as asthma and atopic dermatitis. Modulation of SOCS3 levels in T cells could be useful in regulating the Th1/Th2 balance for the treatment of autoimmune inflammatory diseases.

SOCS and human cancer

Anti-tumor activity of SOCS1 has been reported by several groups. SOCS1 may inhibit the development and/or progression of hepatocellular carcinoma (HCC), because SOCS1 expression is significantly reduced in HCC cells; this can be explained by the inactivation of the SOCS1 promoter due to hypermethylation of CpG islands [81,82]. Yang and colleagues [83] investigated the promoter methylation status of major tumor suppressor genes including SOCS1, GSTP (pi-class glutathione S-transferase), APC (adenomatous polyposis coli), E-cadherin, RAR (retinoic acid receptor)-β, p14, p15, p16 and p73 in 51 cases of HCC. Among these, SOCS1 was the most frequently methylated (65%). Methylation of SOCS1, APC and p15 was more frequently seen in hepatitis C virus-positive HCC than in hepatitis C virus/hepatitis B virus-negative HCC. These data suggest that promoter hypermethylation of SOCS1 is an important event in HCC development. In support of this, a recent experiment has shown that SOCS1 heterozygous mice are hypersensitive to dimethylnitrosamine-induced hepatocarcinogenesis [75]. SOCS1 could be a novel anti-oncogene that accelerates inflammation-induced carcinogenesis. DNA hypermethylation of the SOCS1 gene is also found in several solid tumors derived from the colon, stomach, ovary, lung and breast; however, the frequencies in these tumors are not as high as in HCC [84-91].

In addition, SOCS1 may inhibit the progression of hematopoietic malignancies, because SOCS1 in vivo is preferentially expressed in lymphoid organs. Recent reports have indicated that reduced expression and DNA methylation of SOCS1 are frequently found in myeloma and leukemia cells [92,93]. Interestingly, biallelic mutation in the SOCS box of the SOCS1 gene was found in 9 of 20 primary mediastinal B cell lymphoma cells. These mutations probably result in impaired JAK2 degradation and sustained JAK2 activation [94]. In most cases, SOCS1 overexpression in cell lines could inhibit tumor cell proliferation; SOCS1 could therefore be an important target of anti-tumor therapy.

Like SOCS1, SOCS3 may also be involved in the development and progression of malignancies. In chronic myelogenous leukemia cells, especially in cells in blast crisis and T cell lymphoma, SOCS3 is expressed constitutively and may confer resistance to IFN therapy [95,96]. In contrast, silenced expression of SOCS3 due to hypermethylation has been observed in human lung cancers and may be associated with the progression of cancer cells [97].

Therapeutic application

A next important step of the study of SOCS is a clinical application. Although it is too early to discuss its application to humans, several interesting trials in vitro and in vivo are under way. A group in the University of Florida developed a tyrosine kinase inhibitor peptide, Tkip, that is a mimetic of SOCS1 [98]. This 12-mer peptide interacts specifically with the autophosphorylation site of JAK2 and inhibits IFN-γ signaling. The peptide also suppressed the proliferation of prostate cancer cell lines in which STAT3 is constitutively activated [99]. Further characterization of JAK inhibition by SOCS1-KIR and Tkip peptide may uncover a novel mechanism to suppress the action of a specific cytokine. Overexpression of SOCS3 by adenovirus can prevent mouse RA models [77]. The generation of SOCS proteins carrying membrane-permeable peptide by genetic engineering might be another way to introduce JAK inhibitor into specific cells. The reduction of SOCS expression is also a therapeutic target. siRNA technology made the reduction of SOCS1 expression in DCs possible, and also improved anti-tumor immunity [69]. A decrease in SOCS1 and SOCS3 by antisense RNA treatment in obese diabetic mice improved insulin sensitivity and ameliorated hepatic steatosis and hypertriglyceridemia [100]. These studies are encouraging for controlling cytokine-related pathological conditions by mimicking or modulating SOCS proteins.


SOCS proteins are regulators of cytokine signal transduction and are essential to normal immune physiology, but they also seem to contribute to the development of immunological disorders including inflammatory diseases. Recently accumulated evidence regarding the balance of positive and negative pathways is important for a better understanding of immune systems, and this acquired knowledge will provide new insights that will assist the development of novel therapeutic strategies for both immunological diseases and cancer.


CIS = cytokine-inducible SH2 protein; DC = dendritic cell; G-CSF = granulocyte colony-stimulating factor; GH = growth hormone; HCC = hepato-cellular carcinoma; IFN = interferon; IL = interleukin; IRS = insulin receptor substrate; KIR = kinase inhibitory region; JAK = Janus kinase; KO = knockout; LPS = lipopolysaccharide; NF = nuclear factor; NK = natural killer; RA = rheumatoid arthritis; SH2 = Src homology 2; siRNA = short interfering RNA; SOCS = suppressor of cytokine signaling; STAT = signal transduction and activators of transcription; Th = T helper; TLR = Toll-like receptor; TNF = tumor necrosis factor.

Competing interests

The author(s) declare that they have no competing interests.


  1. Nicola NA: Guidebook to Cytokines and Their Receptors. Oxford: Oxford University Press; 1994.

  2. Ihle JN: Cytokine receptor signaling.

    Nature 1995, 377:591-594. Publisher Full Text OpenURL

  3. O'Shea JJ, Gadina M, Schreiber RD: Cytokine signaling in 2002: new surprises in the Jak/Stat pathway.

    Cell 2002, 109:S121-S131. Publisher Full Text OpenURL

  4. Simoncic PD, Lee-Loy A, Barber DL, Tremblay ML, McGlade CJ: The T cell protein tyrosine phosphatase is a negative regulator of Janus family kinases 1 and 3.

    Curr Biol 2002, 12:446-453. Publisher Full Text OpenURL

  5. Liu B, Mink S, Wong KA, Stein N, Getman C, Dempsey PW, Wu H, Shuai K: PIAS1 selectively inhibits interferon-inducible genes and is important in innate immunity.

    Nat Immunol 2004, 5:891-898. Publisher Full Text OpenURL

  6. Yasukawa H, Sasaki A, Yoshimura A: Negative regulation of cytokine signaling pathways.

    Annu Rev Immunol 2000, 18:143-164. Publisher Full Text OpenURL

  7. Alexander WS: Suppressors of cytokine signalling (SOCS) in the immune system.

    Nat Rev Immunol 2002, 2:410-416. OpenURL

  8. Greenhalgh CJ, Miller ME, Hilton DJ, Lund PK: Suppressors of cytokine signaling: Relevance to gastrointestinal function and disease.

    Gastroenterology 2002, 123:2064-2081. Publisher Full Text OpenURL

  9. Kubo M, Hanada T, Yoshimura A: Suppressors of cytokine signaling and immunity.

    Nat Immunol 2003, 4:1169-1176. Publisher Full Text OpenURL

  10. Alexander WS, Hilton DJ: The role of suppressors of cytokine signaling (SOCS) proteins in regulation of the immune response.

    Annu Rev Immunol 2004, 22:503-529. Publisher Full Text OpenURL

  11. Yoshimura A, Ohkubo T, Kiguchi T, Jenkins NA, Gilbert DJ, Copeland NG, Hara T, Miyajima A: A novel cytokine-inducible gene CIS encodes an SH2-containing protein that binds to tyrosine-phosphorylated interleukin 3 and erythropoietin receptors.

    EMBO J 1995, 14:2816-2826. OpenURL

  12. Ram PA, Waxman DJ: SOCS/CIS protein inhibition of growth hormone-stimulated STAT5 signaling by multiple mechanisms.

    J Biol Chem 1999, 274:35553-35561. Publisher Full Text OpenURL

  13. Greenhalgh CJ, Bertolino P, Asa SL, Metcalf D, Corbin JE, Adams TE, Davey HW, Nicola NA, Hilton DJ, Alexander WS: Growth enhancement in suppressor of cytokine signaling 2 (SOCS-2)-deficient mice is dependent on signal transducer and activator of transcription 5b (STAT5b).

    Mol Endocrinol 2002, 16:1394-1406. Publisher Full Text OpenURL

  14. Metcalf D, Greenhalgh CJ, Viney E, Willson TA, Starr R, Nicola NA, Hilton DJ, Alexander WS: Gigantism in mice lacking suppressor of cytokine signalling-2.

    Nature 2000, 405:1069-1073. Publisher Full Text OpenURL

  15. Seki Y, Hayashi K, Matsumoto A, Seki N, Tsukada J, Ransom J, Naka T, Kishimoto T, Yoshimura A, Kubo M: Expression of the suppressor of cytokine signaling-5 (SOCS5) negatively regulates IL-4-dependent STAT6 activation and Th2 differentiation.

    Proc Natl Acad Sci USA 2002, 99:13003-13008. Publisher Full Text OpenURL

  16. Yasukawa H, Misawa H, Sakamoto H, Masuhara M, Sasaki A, Wakioka T, Ohtsuka S, Imaizumi T, Matsuda T, Ihle JN, et al.: The JAK-binding protein JAB inhibits Janus tyrosine kinase activity through binding in the activation loop.

    EMBO J 1999, 18:1309-1320. Publisher Full Text OpenURL

  17. Giordanetto F, Kroemer RT: A three-dimensional model of Suppressor Of Cytokine Signalling 1 (SOCS-1).

    Protein Eng 2003, 16:115-124. Publisher Full Text OpenURL

  18. Sasaki A, Yasukawa H, Shouda T, Kitamura T, Dikic I, Yoshimura A: CIS3/SOCS-3 suppresses erythropoietin (EPO) signaling by binding the EPO receptor and JAK2.

    J Biol Chem 2000, 275:29338-29347. Publisher Full Text OpenURL

  19. Nicholson SE, De Souza D, Fabri LJ, Corbin J, Willson TA, Zhang JG, Silva A, Asimakis M, Farley A, Nash AD, et al.: Suppressor of cytokine signaling-3 preferentially binds to the SHP-2-binding site on the shared cytokine receptor subunit gp130.

    Proc Natl Acad Sci USA 2000, 97:6493-6498. Publisher Full Text OpenURL

  20. Lehmann U, Schmitz J, Weissenbach M, Sobota RM, Hortner M, Friederichs K, Behrmann I, Tsiaris W, Sasaki A, Schneider-Mergener J, et al.: SHP2 and SOCS3 contribute to Tyr-759-dependent attenuation of interleukin-6 signaling through gp130.

    J Biol Chem 2003, 278:661-671. Publisher Full Text OpenURL

  21. Hortner M, Nielsch U, Mayr LM, Heinrich PC, Haan S: A new high affinity binding site for suppressor of cytokine signaling-3 on the erythropoietin receptor.

    Eur J Biochem 2002, 269:2516-2526. Publisher Full Text OpenURL

  22. Bjorbak C, Lavery HJ, Bates SH, Olson RK, Davis SM, Flier JS, Myers MG Jr: SOCS3 mediates feedback inhibition of the leptin receptor via Tyr985.

    J Biol Chem 2000, 275:40649-40657. Publisher Full Text OpenURL

  23. De Souza D, Fabri LJ, Nash A, Hilton DJ, Nicola NA, Baca M: SH2 domains from suppressor of cytokine signaling-3 and protein tyrosine phosphatase SHP-2 have similar binding specificities.

    Biochemistry 2002, 41:9229-9236. Publisher Full Text OpenURL

  24. Kamura T, Sato S, Haque D, Liu L, Kaelin WG Jr, Conaway RC, Conaway JW: The elongin BC complex interacts with the conserved SOCS-box motif present in members of the SOCS, ras, WD-40 repeat and ankyrin repeat families.

    Genes Dev 1998, 12:3872-3881. OpenURL

  25. Zhang JG, Farley A, Nicholson SE, Willson TA, Zugaro LM, Simpson RJ, Moritz RL, Cary D, Richardson R, Hausmann G, et al.: The conserved SOCS box motif in suppressors of cytokine signaling binds to elongins B and C and may couple bound proteins to proteasomal degradation.

    Proc Natl Acad Sci USA 1999, 96:2071-2076. Publisher Full Text OpenURL

  26. Kamura T, Maenaka K, Kotoshiba S, Matsumoto M, Kohda D, Conaway RC, Conaway JW, Nakayama KI: VHL-box and SOCS-box domains determine binding specificity for Cul2-Rbx1 and Cul5-Rbx2 modules of ubiquitin ligases.

    Genes Dev 2004, 18:3055-3065. Publisher Full Text OpenURL

  27. Kamizono S, Hanada T, Yasukawa H, Minoguchi S, Kato R, Minoguchi M, Hattori K, Hatakeyama S, Yada M, Morita S, et al.: The SOCS box of SOCS-1 accelerates ubiquitin-dependent proteolysis of TEL-JAK2.

    J Biol Chem 2001, 276:12530-12538. Publisher Full Text OpenURL

  28. Frantsve J, Schwaller J, Sternberg DW, Kutok J, Gilliland DG: Socs-1 inhibits TEL-JAK2-mediated transformation of hematopoietic cells through inhibition of JAK2 kinase activity and induction of proteasome-mediated degradation.

    Mol Cell Biol 2001, 21:3547-3557. Publisher Full Text OpenURL

  29. Ungureanu D, Saharinen P, Junttila I, Hilton DJ, Silvennoinen O: Regulation of Jak2 through the ubiquitin-proteasome pathway involves phosphorylation of Jak2 on Y1007 and interaction with SOCS-1.

    Mol Cell Biol 2002, 22:3316-3326. Publisher Full Text OpenURL

  30. Zhang JG, Metcalf D, Rakar S, Asimakis M, Greenhalgh CJ, Willson TA, Starr R, Nicholson SE, Carter W, Alexander WS, et al.: The SOCS box of suppressor of cytokine signaling-1 is important for inhibition of cytokine action in vivo.

    Proc Natl Acad Sci USA 2001, 98:13261-13265. Publisher Full Text OpenURL

  31. De Sepulveda P, Ilangumaran S, Rottapel R: Suppressor of cytokine signaling-1 inhibits VAV function through protein degradation.

    J Biol Chem 2000, 275:14005-14008. Publisher Full Text OpenURL

  32. Kamio M, Yoshida T, Ogata H, Douchi T, Nagata Y, Inoue M, Hasegawa M, Yonemitsu Y, Yoshimura A: SOCS1 inhibits HPV-E7-mediated transformation by inducing degradation of E7 protein.

    Oncogene 2004, 17:3108-3116. OpenURL

  33. Rui L, Yuan M, Frantz D, Shoelson S, White MF: SOCS-1 and SOCS-3 block insulin signaling by ubiquitin-mediated degradation of IRS1 and IRS2.

    J Biol Chem 2002, 277:42394-42398. Publisher Full Text OpenURL

  34. Ueki K, Kondo T, Kahn CR: Suppressor of cytokine signaling 1 (SOCS-1) and SOCS-3 cause insulin resistance through inhibition of tyrosine phosphorylation of insulin receptor substrate proteins by discrete mechanisms.

    Mol Cell Biol 2004, 24:5434-5446. Publisher Full Text OpenURL

  35. Matsumoto A, Seki Y, Kubo M, Ohtsuka S, Suzuki A, Hayashi I, Tsuji K, Nakahata T, Okabe M, Yamada S, et al.: Suppression of STAT5 functions in liver, mammary glands, and T cells in cytokine-inducible SH2-containing protein 1 transgenic mice.

    Mol Cell Biol 1999, 19:6396-6407. OpenURL

  36. Naka T, Matsumoto T, Narazaki M, Fujimoto M, Morita Y, Ohsawa Y, Saito H, Nagasawa T, Uchiyama Y, Kishimoto T: Accelerated apoptosis of lymphocytes by augmented induction of Bax in SSI-1 (STAT-induced STAT inhibitor-1)-deficient mice.

    Proc Natl Acad Sci USA 1998, 95:15577-15582. Publisher Full Text OpenURL

  37. Starr R, Metcalf D, Elefanty AG, Brysha M, Willson TA, Nicola NA, Hilton DJ, Alexander WS: Liver degeneration and lymphoid deficiencies in mice lacking suppressor of cytokine signaling-1.

    Proc Natl Acad Sci USA 1998, 95:14395-14399. Publisher Full Text OpenURL

  38. Marine JC, Topham DJ, McKay C, Wang D, Parganas E, Stravopodis D, Yoshimura A, Ihle JN: SOCS1 deficiency causes a lymphocyte-dependent perinatal lethality.

    Cell 1999, 98:609-616. Publisher Full Text OpenURL

  39. Alexander WS, Alexander WS, Starr R, Fenner JE, Scott CL, Handman E, Sprigg NS, Corbin JE, Cornish AL, Darwiche R, et al.: SOCS1 is a critical inhibitor of interferon-γ signaling and prevents the potentially fatal neonatal actions of this cytokine.

    Cell 1999, 98:597-608. Publisher Full Text OpenURL

  40. Bullen DV, Darwiche R, Metcalf D, Handman E, Alexander WS: Neutralization of interferon-γ in neonatal SOCS1-/- mice prevents fatty degeneration of the liver but not subsequent fatal inflammatory disease.

    Immunology 2001, 104:92-98. Publisher Full Text OpenURL

  41. Roberts AW, Robb L, Rakar S, Hartley L, Cluse L, Nicola NA, Metcalf D, Hilton DJ, Alexander WS: Placental defects and embryonic lethality in mice lacking suppressor of cytokine signaling 3.

    Proc Natl Acad Sci USA 2003, 98:9324-9329. Publisher Full Text OpenURL

  42. Takahashi Y, Carpino N, Cross JC, Torres M, Parganas E, Ihle JN: SOCS3: an essential regulator of LIF receptor signaling in trophoblast giant cell differentiation.

    EMBO J 2003, 22:372-384. Publisher Full Text OpenURL

  43. Yasukawa H, Ohishi M, Mori H, Murakami M, Chinen T, Aki D, Hanada T, Takeda K, Akira S, Hoshijima M, et al.: IL-6 induces an anti-inflammatory response in the absence of SOCS3 in macrophages.

    Nat Immunol 2003, 4:551-556. Publisher Full Text OpenURL

  44. Lang R, Pauleau AL, Parganas E, Takahashi Y, Mages J, Ihle JN, Rutschman R, Murray PJ: SOCS3 regulates the plasticity of gp130 signaling.

    Nat Immunol 2003, 4:546-550. Publisher Full Text OpenURL

  45. Croker BA, Croker BA, Krebs DL, Zhang JG, Wormald S, Willson TA, Stanley EG, Robb L, Greenhalgh CJ, Forster I, et al.: SOCS3 negatively regulates IL-6 signaling in vivo.

    Nat Immunol 2003, 4:540-545. Publisher Full Text OpenURL

  46. Kimura A, Kinjyo I, Matsumura Y, Mori H, Mashima R, Harada M, Chien KR, Yasukawa H, Yoshimura A: SOCS3 is a physiological negative regulator for granulopoiesis and G-CSF receptor signaling.

    J Biol Chem 2004, 297:6905-6910. OpenURL

  47. Croker BA, Metcalf D, Robb L, Wei W, Mifsud S, DiRago L, Cluse LA, Sutherland KD, Hartley L, Williams E, et al.: SOCS3 is a critical physiological negative regulator of G-CSF signaling and emergency granulopoiesis.

    Immunity 2004, 20:153-165. Publisher Full Text OpenURL

  48. Lee CK, Raz R, Gimeno R, Gertner R, Wistinghausen B, Takeshita K, DePinho RA, Levy DE: STAT3 is a negative regulator of gran-ulopoiesis but is not required for G-CSF-dependent differentiation.

    Immunity 2002, 17:63-72. Publisher Full Text OpenURL

  49. Mori H, Hanada R, Hanada T, Aki D, Mashima R, Nishinakamura H, Torisu T, Chien KR, Yasukawa H, Yoshimura A: Socs3 deficiency in the brain elevates leptin sensitivity and confers resistance to diet-induced obesity.

    Nat Med 2004, 10:739-743. Publisher Full Text OpenURL

  50. Howard JK, Cave BJ, Oksanen LJ, Tzameli I, Bjorbaek C, Flier JS: Enhanced leptin sensitivity and attenuation of diet-induced obesity in mice with haploinsufficiency of Socs3.

    Nat Med 2004, 10:734-738. Publisher Full Text OpenURL

  51. Shi H, Tzameli I, Bjorbaek C, Flier JS: Suppressor of cytokine signaling 3 is a physiological regulator of adipocyte insulin signaling.

    J Biol Chem 2004, 279:34733-34740. Publisher Full Text OpenURL

  52. Brender C, Columbus R, Metcalf D, Handman E, Starr R, Huntington N, Tarlinton D, Odum N, Nicholson SE, Nicola NA, et al.: SOCS5 is expressed in primary B and T lymphoid cells but is dispensable for lymphocyte production and function.

    Mol Cell Biol 2004, 24:6094-6103. Publisher Full Text OpenURL

  53. Callus BA, Mathey-Prevot B: SOCS36E, a novel Drosophila SOCS protein, suppresses JAK/STAT and EGF-R signalling in the imaginal wing disc.

    Oncogene 2002, 21:4812-4821. Publisher Full Text OpenURL

  54. Krebs DL, Uren RT, Metcalf D, Rakar S, Zhang JG, Starr R, De Souza DP, Hanzinikolas K, Eyles J, Connolly LM, et al.: SOCS-6 binds to insulin receptor substrate 4, and mice lacking the SOCS-6 gene exhibit mild growth retardation.

    Mol Cell Biol 2002, 22:4567-4578. Publisher Full Text OpenURL

  55. Krebs DL, Metcalf D, Merson TD, Voss AK, Thomas T, Zhang JG, Rakar S, O'Bryan MK, Willson TA, Viney EM, et al.: Development of hydrocephalus in mice lacking SOCS7.

    Proc Natl Acad Sci USA 2004, 101:15446-15451. Publisher Full Text OpenURL

  56. Metcalf D, Mifsud S, Di Rago L, Nicola NA, Hilton DJ, Alexander WS: Polycystic kidneys and chronic inflammatory lesions are the delayed consequences of loss of the suppressor of cytokine signaling-1 (SOCS-1).

    Proc Natl Acad Sci USA 2002, 99:943-948. Publisher Full Text OpenURL

  57. Naka T, Tsutsui H, Fujimoto M, Kawazoe Y, Kohzaki H, Morita Y, Nakagawa R, Narazaki M, Adachi K, Yoshimoto T, et al.: SOCS-1/ SSI-1-deficient NKT cells participate in severe hepatitis through dysregulated cross-talk inhibition of IFN- and IL-4 signaling in vivo.

    Immunity 2001, 14:535-545. Publisher Full Text OpenURL

  58. Chong MM, Cornish AL, Darwiche R, Stanley EG, Purton JF, Godfrey DI, Hilton DJ, Starr R, Alexander WS, Kay TW: Suppressor of cytokine signaling-1 is a critical regulator of interleukin-7-dependent CD8+ T cell differentiation.

    Immunity 2003, 18:475-487. Publisher Full Text OpenURL

  59. Crepso A, Filla MB, Russell SW, Murphy WJ: Indirect induction of suppressor of cytokine signaling-1 in macrophages stimulated with bacterial lipopolysaccharide: partial role of autocrine/paracrine interferon-alpha/beta.

    Biochem J 2000, 349:99-104. Publisher Full Text OpenURL

  60. Bode JG, Nimmesgern A, Schmitz J, Schaper F, Schmitt M, Frisch W, Haussinger D, Heinrich PC, Graeve L: LPS and TNFalpha induce SOCS3 mRNA and inhibit IL-6-induced activation of STAT3 in macrophages. LPS and TNFalpha induce SOCS3 mRNA and inhibit IL-6-induced activation of STAT3 in macrophages.

    FEBS Lett 1999, 463:365-370. Publisher Full Text OpenURL

  61. Dalpke AH, Opper S, Zimmermann S, Heeg K: Suppressors of cytokine signaling (SOCS)-1 and SOCS-3 are induced by CpG-DNA and modulate cytokine responses in APCs.

    J Immunol 2001, 166:7082-7089. OpenURL

  62. Kinjyo I, Hanada T, Inagaki-Ohara K, Mori H, Aki D, Ohishi M, Yoshida H, Kubo M, Yoshimura A: SOCS1/JAB is a negative regulator of LPS-induced macrophage activation.

    Immunity 2002, 17:583-591. Publisher Full Text OpenURL

  63. Nakagawa R, Naka T, Tsutsui H, Fujimoto M, Kimura A, Abe T, Seki E, Sato S, Takeuchi O, Takeda K, et al.: SOCS-1 participates in negative regulation of LPS responses.

    Immunity 2002, 17:677-687. Publisher Full Text OpenURL

  64. Gingras S, Parganas E, de Pauw A, Ihle JN, Murray PJ: Re-examination of the role of suppressor of cytokine signaling 1 (SOCS1) in the regulation of Toll-like receptor signaling.

    J Biol Chem 2004, 279:54702-54707. Publisher Full Text OpenURL

  65. Baetz A, Frey M, Heeg K, Dalpke AH: Suppressor of cytokine signaling (SOCS) proteins indirectly regulate toll-like receptor signaling in innate immune cells.

    J Biol Chem 2004, 279:54708-54715. Publisher Full Text OpenURL

  66. Ryo A, Suizu F, Yoshida Y, Perrem K, Liou YC, Wulf G, Rottapel R, Yamaoka S, Lu KP: Regulation of NF-kappaB signaling by Pin1-dependent prolyl isomerization and ubiquitin-mediated proteolysis of p65/RelA.

    Mol Cell 2003, 12:1413-1426. Publisher Full Text OpenURL

  67. Hanada T, Yoshida H, Kato S, Tanaka K, Masutani K, Tsukada J, Nomura Y, Mimata H, Kubo M, Yoshimura A: Suppressor of cytokine signaling-1 is essential for suppressing dendritic cell activation and systemic autoimmunity.

    Immunity 2003, 19:437-450. Publisher Full Text OpenURL

  68. Hanada T, Tanaka K, Matsumura Y, Yamauchi M, Nishinakamura H, Aburatani H, Mashima R, Kubo M, Kobayashi T, Yoshimura A: Induction of hyper T-helper 1 (Th1) cell type immune responses by dendritic cells lacking the suppressors of cytokine signaling-1 (SOCS1) gene.

    J Immunol 2005, 174:4325-4332. OpenURL

  69. Shen L, Evel-Kabler K, Strube R, Chen SY: Silencing of SOCS1 enhances antigen presentation by dendritic cells and antigen-specific anti-tumor immunity.

    Nat Biotechnol 2004, 22:1546-1553. Publisher Full Text OpenURL

  70. Takeda K, Clausen BE, Kaisho T, Tsujimura T, Terada N, Forster I, Akira S: Enhanced Th1 activity and development of chronic enterocolitis in mice devoid of Stat3 in macrophages and neutrophils.

    Immunity 1999, 10:39-49. Publisher Full Text OpenURL

  71. Egan PJ, Lawlor KE, Alexander WS, Wicks IP: Suppressor of cytokine signaling-1 regulates acute inflammatory arthritis and T cell activation.

    J Clin Invest 2003, 111:915-924. Publisher Full Text OpenURL

  72. Ivashkiv LB, Tassiulas I: Can SOCS make arthritis better?

    J Clin Invest 2003, 111:795-797. Publisher Full Text OpenURL

  73. Yamana J, Yamamura M, Okamoto A, Aita T, Iwahashi M, Sunahori K, Makino H: Resistance to IL-10 inhibition of interferon gamma production and expression of suppressor of cytokine signaling 1 in CD4+ T cells from patients with rheumatoid arthritis.

    Arthritis Res Ther 2004, 6:R567-577. BioMed Central Full Text OpenURL

  74. de Hooge AS, van de Loo FA, Koenders MI, Bennink MB, Arntz OJ, Kolbe T, van den Berg WB: Local activation of STAT-1 and STAT-3 in the inflamed synovium during zymosan-induced arthritis: exacerbation of joint inflammation in STAT-1 gene-knockout mice.

    Arthritis Rheum 2004, 50:2014-2023. Publisher Full Text OpenURL

  75. Yoshida T, Ogata H, Kamio M, Joo A, Shiraishi H, Tokunaga Y, Sata M, Nagai H, Yoshimura A: SOCS1 is a suppressor of liver fibrosis and hepatitis-induced carcinogenesis.

    J Exp Med 2004, 199:1701-1707. Publisher Full Text OpenURL

  76. Suzuki A, Hanada T, Mitsuyama K, Yoshida T, Kamizono S, Hoshino T, Kubo M, Yamashita A, Okabe M, Takeda K: CIS3/SOCS3/SSI3 plays a negative regulatory role in STAT3 activation and intestional inflammation.

    J Exp Med 2001, 193:471-481. Publisher Full Text OpenURL

  77. Shouda T, Yoshida T, Hanada T, Wakioka T, Oishi M, Miyoshi K, Komiya S, Kosai K, Hanakawa Y, Hashimoto K: Induction of the cytokine signal regulator SOCS3/CIS3 as a therapeutic strategy for treating inflammatory arthritis.

    J Clin Invest 2001, 108:1781-1788. Publisher Full Text OpenURL

  78. Atsumi T, Ishihara K, Kamimura D, Ikushima H, Ohtani T, Hirota S, Kobayashi H, Park SJ, Saeki Y, Kitamura Y, et al.: A point mutation of Tyr-759 in interleukin 6 family cytokine receptor subunit gp130 causes autoimmune arthritis.

    J Exp Med 2002, 196:979-990. Publisher Full Text OpenURL

  79. Tebbutt NC, Giraud AS, Inglese M, Jenkins B, Waring P, Clay FJ, Malki S, Alderman BM, Grail D, Hollande F, et al.: Reciprocal regulation of gastrointestinal homeostasis by SHP2 and STAT-mediated trefoil gene activation in gp130 mutant mice.

    Nat Med 2002, 8:1089-1097. Publisher Full Text OpenURL

  80. Seki Y, Inoue H, Nagata N, Hayashi K, Fukuyama S, Matsumoto K, Komine O, Hamano S, Himeno K, Inagaki-Ohara K, et al.: SOCS-3 regulates onset and maintenance of TH2-mediated allergic responses.

    Nat Med 2003, 9:1047-1054. Publisher Full Text OpenURL

  81. Yoshikawa H, Matsubara K, Qian GS, Jackson P, Groopman JD, Manning JE, Harris CC, Herman JG: SOCS-1, a negative regulator of the JAK/STAT pathway, is silenced by methylation in human hepatocellular carcinoma and shows growth-suppression activity.

    Nat Genet 2001, 28:29-35. Publisher Full Text OpenURL

  82. Nagai H, Kim YS, Konishi N, Baba M, Kubota T, Yoshimura A, Emi M: Combined hypermethylation and chromosome loss associated with inactivation of SSI-1/SOCS-1/JAB gene in human hepatocellular carcinomas.

    Cancer Lett 2002, 186:59-65. Publisher Full Text OpenURL

  83. Yang B, Guo M, Herman JG, Clark DP: Aberrant promoter methylation profiles of tumor suppressor genes in hepatocellular carcinoma.

    Am J Pathol 2003, 163:1101-1107. OpenURL

  84. Takahashi T, Shivapurkar N, Riquelme E, Shigematsu H, Reddy J, Suzuki M, Miyajima K, Zhou X, Bekele BN, Gazdar AF, et al.: Aberrant promoter hypermethylation of multiple genes in gall-bladder carcinoma and chronic cholecystitis.

    Clin Cancer Res 2004, 10:6126-6133. OpenURL

  85. Bai AH, Tong JH, To KF, Chan MW, Man EP, Lo KW, Lee JF, Sung JJ, Leung WK: Promoter hypermethylation of tumor-related genes in the progression of colorectal neoplasia.

    Int J Cancer 2004, 112:846-853. Publisher Full Text OpenURL

  86. Oshimo Y, Kuraoka K, Nakayama H, Kitadai Y, Yoshida K, Chayama K, Yasui W: Epigenetic inactivation of SOCS-1 by CpG island hypermethylation in human gastric carcinoma.

    Int J Cancer 2004, 112:1003-1009. Publisher Full Text OpenURL

  87. Sutherland KD, Lindeman GJ, Choong DY, Wittlin S, Brentzell L, Phillips W, Campbell IG, Visvader JE: Differential hypermethylation of SOCS genes in ovarian and breast carcinomas.

    Oncogene 2004, 23:7726-7733. Publisher Full Text OpenURL

  88. To KF, Chan MW, Leung WK, Ng EK, Yu J, Bai AH, Lo AW, Chu SH, Tong JH, Lo KW, Sung JJ, Chan FK: Constitutional activation of IL-6-mediated JAK/STAT pathway through hypermethylation of SOCS-1 in human gastric cancer cell line.

    Br J Cancer 2004, 91:1335-1341. OpenURL

  89. Komazaki T, Nagai H, Emi M, Terada Y, Yabe A, Jin E, Kawanami O, Konishi N, Moriyama Y, Naka T, et al.: Hypermethylation-associated inactivation of the SOCS-1 gene, a JAK/STAT inhibitor, in human pancreatic cancers.

    Jpn J Clin Oncol 2004, 34:191-194. Publisher Full Text OpenURL

  90. Fujitake S, Hibi K, Okochi O, Kodera Y, Ito K, Akiyama S, Nakao A: Aberrant methylation of SOCS-1 was observed in younger colorectal cancer patients.

    J Gastroenterol 2004, 39:120-124. Publisher Full Text OpenURL

  91. Lin SY, Yeh KT, Chen WT, Chen HC, Chen ST, Chiou HY, Chang JG: Promoter CpG methylation of tumor suppressor genes in colorectal cancer and its relationship to clinical features.

    Oncol Rep 2004, 11:341-348. OpenURL

  92. Watanabe D, Ezoe S, Fujimoto M, Kimura A, Saito Y, Nagai H, Tachibana I, Matsumura I, Tanaka T, Kanegane H, et al.: Suppressor of cytokine signalling-1 gene silencing in acute myeloid leukaemia and human haematopoietic cell lines.

    Br J Haematol 2004, 126:726-735. Publisher Full Text OpenURL

  93. Galm O, Wilop S, Reichelt J, Jost E, Gehbauer G, Herman JG, Osieka R: DNA methylation changes in multiple myeloma.

    Leukemia 2004, 18:1687-1692. Publisher Full Text OpenURL

  94. Melzner I, Bucur AJ, Bruderlein S, Dorsch K, Hasel C, Barth TF, Leithauser F, Moller P: Biallelic mutation of SOCS-1 impairs JAK2 degradation and sustains phospho-JAK2 action in MedB-1 mediastinal lymphoma line.

    Blood 2004, 105:2535-2542. Publisher Full Text OpenURL

  95. Brender C, Lovato P, Sommer VH, Woetmann A, Mathiesen AM, Geisler C, Wasik M, Odum N: Constitutive SOCS-3 expression protects T-cell lymphoma against growth inhibition by IFNalpha.

    Leukemia 2005, 19:209-213. Publisher Full Text OpenURL

  96. Sakai I, Takeuchi K, Yamauchi H, Narumi H, Fujita S: Constitutive expression of SOCS3 confers resistance to IFN-alpha in chronic myelogenous leukemia cells.

    Blood 2002, 100:2926-2931. Publisher Full Text OpenURL

  97. He B, You L, Uematsu K, Zang K, Xu Z, Lee AY, Costello JF, McCormick F, Jablons DM: SOCS-3 is frequently silenced by hypermethylation and suppresses cell growth in human lung cancer.

    Proc Natl Acad Sci USA 2003, 100:14133-14138. Publisher Full Text OpenURL

  98. Flowers LO, Johnson HM, Mujtaba MG, Ellis MR, Haider SM, Subramaniam PS: Characterization of a peptide inhibitor of Janus kinase 2 that mimics suppressor of cytokine signaling 1 function.

    J Immunol 2004, 172:7510-7518. OpenURL

  99. Flowers LO, Subramaniam PS, Johnson HM: A SOCS-1 peptide mimetic inhibits both constitutive and IL-6 induced activation of STAT3 in prostate cancer cells.

    Oncogene 2005, 24:2114-2120. Publisher Full Text OpenURL

  100. Ueki K, Kondo T, Tseng YH, Kahn CR: Central role of suppressors of cytokine signaling proteins in hepatic steatosis, insulin resistance, and the metabolic syndrome in the mouse.

    Proc Natl Acad Sci USA 2004, 101:10422-10427. Publisher Full Text OpenURL