SOCS Proteins Research Articles

The Role of Hepatic Expression of STAT1, SOCS3 and PIAS1 in the Response of Chronic Hepatitis C Patients to Therapy

The underlying mechanisms of hepatitis C virus (HCV) resistance to treatment are unknown. Signal transducers and activators of transcription (STAT) proteins play a critical role in antiviral defense. To explore some of the mechanisms of HCV resistance to interferon, the expression of STAT1 and its negative regulators, protein inhibitor of activated STAT (PIAS1) and suppressor of cytokine signalling (SOCS3), in liver tissues of both inteferon responders and nonresponders in chronic HCV patients. Sixty patients were divided into the following groups: group 1a comprised 38 treatment-responder chronic HCV patients; group 1b consisted of 22 treatment-nonresponder chronic HCV patients; and group 2 consisted of six control subjects. Liver biopsies were examined for histological scoring; STAT1, SOCS3 and PIAS1 expression was analyzed using Western blotting methods. STAT1 expression in the liver tissue of patients in group 1 was significantly increased compared with group 2 patients (P=0.001), while no significant difference in expression was observed between group 1a and group 1b patients (P=0.747). However, phosphorylated STAT1 protein was expressed at a significantly higher level in liver tissue of patients in group 1a compared with patients in group 1b (P=0.001). Western blot analysis of PIAS1 and SOCS3 protein expression in liver tissues from groups 1 and 2 revealed significantly increased expression in group 1 compared with group 2 (P=0.001). In addition, PIAS1 and SOCS3 protein expression was significantly higher in the liver tissues of patients in group 1b compared with patients in group 1a. Levels of STAT1 and⁄or the protein expression of its negative regulators, PIAS1 and SOCS3, may be a good predictor of response to therapy. These could be used as biomarkers that are easily detected by Western blotting or immunostaining during standard histopathological liver biopsy analysis.

STAT3 modulates cigarette smoke-induced inflammation and protease expression

Signal transducer and activator of transcription-3 (STAT3) regulates inflammation, apoptosis, and protease expression, which are critical processes associated with airway injury and lung tissue destruction. However, the precise role of STAT3 in the development of airway diseases such as chronic obstructive pulmonary disease (COPD) has not been established. This study shows that cigarette smoke activates STAT3 in the lungs of mice. Since cigarette smoke activated STAT3 in the lung, we then evaluated how the loss of STAT3 would impact on smoke-mediated lung inflammation, protease expression, and apoptosis. STAT3+/+ and STAT3−/− mice were exposed to 8 days of cigarette smoke. Compared to the STAT3+/+ mice bronchoalveolar lavage fluid (BALF) cellularity was significantly elevated in the STAT3−/− mice both before and after cigarette smoke exposure, with the increase in cells primarily macrophages. In addition, smoke exposure induced significantly higher BALF protein levels of Interleukin-1α (IL-1α), and monocyte chemotactic protein-1 (MCP-1) and higher tissue expression of keratinocyte chemoattractant (KC) in the STAT3−/− mice. Lung mRNA expression of MMP-12 was increased in STAT3−/− at baseline. However, the smoke-induced increase in MMP-10 expression seen in the STAT3+/+ mice was not observed in the STAT3−/− mice. Moreover, lung protein levels of the anti-inflammatory proteins SOCS3 and IL-10 were markedly lower in the STAT3−/− mice compared to the STAT3+/+ mice. Lastly, apoptosis, as determined by caspase 3/7 activity assay, was increased in the STAT3−/− at baseline to levels comparable to those observed in the smoke-exposed STAT3+/+ mice. Together, these results indicate that the smoke-mediated induction of lung STAT3 activity may play a critical role in maintaining normal lung homeostasis and function.

Misregulation of suppressors of cytokine signaling in eosinophilic esophagitis

Several findings suggest that eosinophilic esophagitis (EoE) is strongly associated with atopy and allergen-driven, Th2-type immune responses, indicating the association of EoE with immune dysregulation. The objective of this study is to ascertain the molecular mechanism involved in EoE disease development a Th2 condition. 25 patients with diagnosis of EoE and 17 non-EoE controls were recruited by the gastroenterology and allergy departments from three different hospitals. Transcription analysis of suppressors of cytokine signaling 1, 3, 5 (SOCS), interleukin-5 (IL), IL-13, eotaxin (CCL26), eoataxin receptor (CCR3), and mitogen-activated protein kinase 1 (MAPK1) was performed in esophageal biopsies by real time PCR. Western blot of ERK esophageal protein and additional measures of IL-5 and VEGF levels in serum were performed. The esophagus of EoE patients expresses and synthesizes high levels of SOCS1 and SOCS3 proteins (P<0.05), and these expression correlated with levels of IL-5, IL-13, CCL26, CCR3, and MAPK1 genes. In addition, we demonstrate the implication of the ERK pathway (P<0.001). SOCS proteins probably contribute to EoE pathogenesis by directly or indirectly inducing the Th2 profile, as well as by promoting the production of Th2 cytokines. All these findings further enhance our understanding of the mechanism of EoE, and accumulating evidence suggests that EoE pathogenesis is likely to be due to misregulation of immunological pathways.

Cycloheximide stimulates suppressor of cytokine signaling-3 gene expression in 3T3-L1 adipocytes via the extracellular signal-regulated kinase pathway

Suppressor of cytokine signaling (SOCS)-3 can act as a regulator of energy metabolism and cytokine signaling in fat cells. It is regulated by hormones and toxicological factors. However, the action of cycloheximide on expression of adipocyte SOCS-3 gene is unknown. Using 3T3-L1 adipocytes, we found that cycloheximide up-regulated SOCS-3 mRNA expression in dose- and time-dependent manners. Treatment with actinomycin D prevented cycloheximide-stimulated SOCS-3 mRNA expression, suggesting that the effect of cycloheximide requires new mRNA synthesis. While cycloheximide was shown to increase activities of MEK1 and JNK, signaling was demonstrated to be inhibited by pretreatment with either MEK1 inhibitors U0126 and PD98059, or with the JNK inhibitor SP600125. U0126 and PD98059, respectively, reduced cycloheximide-stimulated SOCS-3 mRNA expression, but SP600125 did not antagonize cycloheximide effect. Moreover, cycloheximide was observed to up-regulate expression of other SOCS family members, such as SOCS-1, -2, -4, -5, -6, -7, and cytokine-inducible SH2-containing protein (CIS)-1 mRNAs. Such effects varied with the dosage and duration of cycloheximide treatment. These results imply the functional MEK1/ERK-mediated pathway is necessary for the cycloheximide stimulation of SOCS-3 gene expression.

Expression of suppressor of cytokine signaling in peripheral blood monocular cells of patients with sympathetic ophthalmia

Objective To investigate the mRNA and protein expression of suppressor of cytokine signaling (SOCS) in peripheral blood mononuclear cells(PBMC) of patients with sympathetic ophthalmia.Methods Blood samples were taken from 14 sympathetic ophthalmia patients with active uveitis,13 quiescent patients,and 15 healthy individuals.IFN-γ,IL-12 and IL-4 in the serum were measured by ELISA.PBMC were subjected to analysis of SOCS mRNA and protein expression using quantitative RT-PCR and western blot,respectively.Results The level of IFN-γ,IL-12 and IL-4 were all significantly higher in the serum of sympathetic ophthalmia patients with active uveitis than that in controls and quiescent patients(P ＜0.05).There were no significant differences between the quiescent patients and the controls(P ＞ 0.05).Compared to healthy volunteers,the expressions of cytokine inducible SH2 containing protein (CIS),SOCS1,SOCS3 and SOCS5 mRNA and protein were significantly increased.There were no significant differences in expression of CIS,SOCS1,SOCS3 mRNA and protein in quiescent patients,but SOCS5 mRNA and protein were significantly increased.Conclusion Up regulation of SOCS1 and SOCS5 expression may involve in the development of a Th1 mediated immune response in sympathetic ophthalmia patients with active uveitis.CIS and SOCS3 may play important roles in mitigating the pathogenic effects of proinflammatory cytokines.It were kept balance in quiescent patients,and up-regulation of SOCS5 may have protective functions. Key words: Suppressor of cytokine signaling; Sympathetic ophthalmia

SOCS3 promotes interleukin-17 expression of human T cells

AbstractSOCS3 is a feedback regulator of cytokine signaling that affects T-cell polarization. Human tuberculosis is accompanied by increased SOCS3 expression in T cells, and this may influence susceptibility against Mycobacterium tuberculosis. Because the role of SOCS3 in human T-cell function is not well defined, we characterized cytokine expression and proliferation of human T cells with differential SOCS3 expression in the present study. We established a flow cytometry–based method for SOCS3 protein quantification and detected higher SOCS3 levels induced by M tuberculosis specific T-cell activation and a transient decrease of SOCS3 expression in the presence of mycobacteria-infected macrophages. Notably increased SOCS3 expression was detected in IL-17–expressing T-cell clones and in CD161+ T helper type 17 cells ex vivo. Ectopic SOCS3 expression in primary CD4+ T cells by lentiviral transduction induced increased IL-17 production but diminished proliferation and viability. Recombinant IL-7 inhibited SOCS3 expression and reduced IL-17–expressing T-cell proportions. We concluded that higher SOCS3 expression in human T cells favors T helper type 17 cells. Therefore, increased SOCS3 expression in human tuberculosis may reflect polarization toward IL-17–expressing T cells as well as T-cell exhaustion marked by reduced proliferation.

Identification of miR-30d as a novel prognostic maker of prostate cancer

Prostate cancer (PCa) is the most common malignant carcinoma that develops in men in Western countries. MicroRNA (miRNA) have the potential to be used as biomarkers and therapeutic targets for the treatment of various cancers. We found significantly higher expression of miR-30d in 3 PCa cell lines (PC3, DU145 and LNCaP) compared with 2 normal prostate cell lines (RWPE-1 and PrSc) using miRNA microarrays and qPCR. Clinicopathological study revealed that miR-30d expression levels were significantly higher in cancer tissue samples than in the paired normal controls (P = 0.03). Furthermore, the miR-30d-high group had shorter time to biochemical recurrence (P = 0.026). MiR-30d overexpressed PCa cells promoted proliferation and invasion in vitro. Inoculation of miR-30d depleted PCa cells dramatically reduced tumor volumes in vivo. Using reporter gene assay, we identified miR-30d as a downregulator of SOCS1 expression by directly binding to 3'-UTR of SOCS1. MiR-30d regulated the expression of phospho-STAT3, MMP-2 and MMP-9 through the downregulation of SOCS1. The levels of SOCS1 mRNA and protein were significantly down-regulated in prostate cancer tissues. Consistently, miR-30d expression was inversely correlated with SOCS1 expression (P = 0.03). The miR-30d-high/SOCS1-low group was associated with an increased risk of early biochemical recurrence (P = 0.0057). Taken together, miR-30d appears to be a novel independent prognostic marker of PCa progression that allows clinicians to identify patients who need more intensive treatments.

T(8;9)(p22;p24)/PCM1-JAK2 Activates SOCS2 and SOCS3 Via STAT5

AbstractAbstract 1567Fusions of the tyrosine kinase domain of JAK2 with multiple partners occur in leukemia/lymphoma where they are believed to promote JAK2-oligomerization and autonomous signalling although the underlying mechanisms remain unclear. Affected entities are candidates for therapy with JAK2 signalling inhibitors. Among 200 peripheral T-cell lymphomas surveyed, we identified only two with JAK2 amplification and none with JAK2 translocations, confirming their rarity in T-cell neoplasias. Here we describe the genomic, transcriptional and signalling characteristics of PCM1-JAK2 formed by t(8;9)(p22;p24) in cell lines established at indolent and aggressive phases of a cutaneous T-cell lymphoma. To investigate signalling, PCM1-JAK2 was subjected to lentiviral knockdown which inhibited 7 genes most upregulated in t(8;9) cells, notably SOCS2/3. SOCS3, but not SOCS2, was also upregulated in a chronic eosinophilic leukemia bearing PCM1-JAK2. Conversely, expression of GATA3, a key T-cell developmental gene silenced in aggressive phase cells, was partially restored by PCM1-JAK2 knockdown. Activation of the tumor suppressor SOCS3 by PCM1-JAK2 may follow structural alteration of JAK2 affecting the ternary complex it forms with SOCS3 and receptor proteins. Treatment with JAK2 inhibitor (TG101348) to which MAC-1/2A/2B cells were conspicuously sensitive mimicked knockdown results, highlighting JAK2 as the active moiety. PCM1-JAK2 signalling required pSTAT5 as reported for JAK2V617F or ETV6/TEL-JAK2, thus extending the paradigm of STAT5 activation by JAK2 alterations in hematopoietic malignancies. MAC-1/2A/2B are the first JAK2– translocation cell line models. Our data support further investigation of SOCS2/3 as signalling effectors, prognostic indicators and potential therapeutic targets in cancers with JAK2 rearrangements. Disclosures:No relevant conflicts of interest to declare.

Role of SOCS3 Evaluated by Immunohistochemical Analysis in a Cohort of Patients Affected by Prostate Cancer: Preliminary Results

Chronic inflammation may play a role in prostate carcinogenesis. Molecular alterations of the Suppressor of Cytokine Signaling (SOCS)-3 can contribute to explain the pleiotropic role of interleukin (IL)-6 in this type of cancer. Recently, the methylation of SOCS3 gene has been demonstrated to cause the non-expression of the protein, being involved in the pathogenesis of prostate cancer (PC) and identifying a subset of aggressive tumors. We evaluated the expression of SOCS3 protein in patients (pt) with bioptically-diagnosed PC by immunohistochemical analysis, which is easier to perform, cheaper and more reproducible compared to DNA analysis. We analyzed the protein expression of SOCS3 by immunohistochemistry in 44 patients (pt) with PC diagnosed after biopsy. Slides were incubated with monoclonal antibody SOCS3 (1E4, 1.5 μg/mL; Abnova, Taiwan). The SOCS3 staining intensity was evaluated by two pathologists (FP and LML) in three different ways: positive (+), negative (-) and weak (+/-). Colonic mucosa was used as positive control. 36/44 patients underwent radical prostatectomy (RP). Biopsy Gleason score (Gs) was: <7 in 8 pt, 7 in 33 pt (3 + 4 pattern in 21 pt, 4 + 3 pattern in 12 pt), >7 in 3 pt. 8/8 (100%) pt with Gs <7 and 7/33 (21%) with Gs 7 were SOCS+. 15/33 (45%) pt with Gs 7 and 3/3 (100%) pt with Gs >7 were negative. In 11/33 pt (33%) Gs 7 a weak intensity was found so they were classified as SOCS3 +/-.25/36 (69%) patients who underwent RP were SOCS3- (15 pt with Gs 7(3 + 4), 7 pt with Gs 7(4 + 3), 3 pt with Gs 8) and 11/36 (30%) SOCS3+ (8 pt with Gs 6 and 3 pt with Gs 7(3 + 4)) (Tab 2). 12/25 (48%) SOCS3- pt had an organ-confined disease (≤pT2), whereas 13/25 (52%) had an extra prostatic neoplasm (5 pT3a (one was N+), 6 pT3b, 1 pT4). All SOCS3+ patients (8/8 (100%)) had an organ-confined disease. 3/3 (100%) SOCS3+/- pt had an extra prostatic neoplasm (>pT2). SOCS3- pt turned out to have a more aggressive disease compared with SOCS3+. In particular, also SOCS3+/- patients seemed to have an aggressive behavior. The non-expression of SOCS3 protein may identify PC with more aggressive behavior and can be evaluated with immunohystochemical analysis, which is a relatively easy and cheap procedure in clinical practice. These results, if confirmed by a wider population and a longer follow-up, may encourage the research on the use of this molecular family as a prognostic marker and a target for therapy with demethylating agents.

Proteasomal Degradation of Nod2 Protein Mediates Tolerance to Bacterial Cell Wall Components

The innate immune system serves as the first line of defense by detecting microbes and initiating inflammatory responses. Although both Toll-like receptor (TLR) and nucleotide binding domain and leucine-rich repeat (NLR) proteins are important for this process, their excessive activation is hazardous to hosts; thus, tight regulation is required. Endotoxin tolerance is refractory to repeated lipopolysaccharide (LPS) stimulation and serves as a host defense mechanism against septic shock caused by an excessive TLR4 response during gram-negative bacterial infection. Gram-positive bacteria as well as their cell wall components also induce shock. However, the mechanism underlying tolerance is not understood. Here, we show that activation of Nod2 by its ligand, muramyl dipeptide (MDP) in the bacterial cell wall, induces rapid degradation of Nod2, which confers MDP tolerance in vitro and in vivo. Nod2 is constitutively associated with a chaperone protein, Hsp90, which is required for Nod2 stability and protects Nod2 from degradation. Upon MDP stimulation, Hsp90 rapidly dissociates from Nod2, which subsequently undergoes ubiquitination and proteasomal degradation. The SOCS-3 protein induced by Nod2 activation further facilitates this degradation process. Therefore, Nod2 protein stability is a key factor in determining responsiveness to MDP stimulation. This indicates that TLRs and NLRs induce a tolerant state through distinct molecular mechanisms that protect the host from septic shock.

Gemfibrozil, a Lipid-lowering Drug, Induces Suppressor of Cytokine Signaling 3 in Glial Cells: IMPLICATIONS FOR NEURODEGENERATIVE DISORDERS

Glial inflammation is an important feature of several neurodegenerative disorders. Suppressor of cytokine signaling (SOCS) proteins play a crucial role in inhibiting cytokine signaling and inflammatory gene expression in various cell types, including glial cells. However, mechanisms by which SOCS genes could be up-regulated are poorly understood. This study underlines the importance of gemfibrozil, a Food and Drug Administration-approved lipid-lowering drug, in up-regulating the expression of SOCS3 in glial cells. Gemfibrozil increased the expression of Socs3 mRNA and protein in mouse astroglia and microglia in both a time- and dose-dependent manner. Interestingly, gemfibrozil induced the activation of type IA phosphatidylinositol (PI) 3-kinase and AKT. Accordingly, inhibition of PI 3-kinase and AKT by chemical inhibitors abrogated gemfibrozil-mediated up-regulation of SOCS3. Furthermore, we demonstrated that gemfibrozil induced the activation of Krüppel-like factor 4 (KLF4) via the PI 3-kinase-AKT pathway and that siRNA knockdown of KLF4 abrogated gemfibrozil-mediated up-regulation of SOCS3. Gemfibrozil also induced the recruitment of KLF4 to the distal, but not proximal, KLF4-binding site of the Socs3 promoter. This study delineates a novel property of gemfibrozil in up-regulating SOCS3 in glial cells via PI 3-kinase-AKT-mediated activation of KLF4 and suggests that gemfibrozil may find therapeutic application in neuroinflammatory and neurodegenerative disorders.

Constitutive Phosphorylation of Interferon Receptor A-Associated Signaling Proteins in Systemic Lupus Erythematosus

BackgroundOverexpression of type I interferon (IFN-I)-induced genes is a common feature of systemic lupus erythematosus (SLE) and its experimental models, but the participation of endogenous overproduction of IFN-I on it is not clear. To explore the possibility that abnormally increased IFN-I receptor (IFNAR) signaling could participate in IFN-I-induced gene overexpression of SLE, we examined the phosphorylation status of the IFNAR-associated signaling partners Jak1 and STAT2, and its relation with expression of its physiologic inhibitor SOCS1 and with plasma levels of IFNα and IFN-like activity.Methodology/Principal FindingsPeripheral blood mononuclear cells (PBMC) from SLE patients with or without disease activity and healthy controls cultured in the presence or in the absence of IFNβ were examined by immunoprecipitation and/or western blotting for expression of the two IFNAR chains, Jak1, Tyk2, and STAT2 and their phosphorylated forms. In SLE but not in healthy control PBMC, Jak1 and STAT2 were constitutively phosphorylated, even in the absence of disease activity (basal pJak1: controls vs. active SLE p<0.0001 and controls vs. inactive SLE p = 0.0006; basal pSTAT2: controls vs. active and inactive SLE p<0.0001). Although SOCS1 protein was slightly but significantly decreased in SLE in the absence or in the presence of IFNβ (p = 0.0096 to p<0.0001), in SOCS1 mRNA levels were markedly decreased (p = 0.036 to p<0.0001). IFNβ induced higher levels of the IFN-I-dependent MxA protein mRNA in SLE than in healthy controls, whereas the opposite was observed for SOCS1. Although there was no relation to increased serum IFNα, active SLE plasma could induce expression of IFN-dependent genes by normal PBMC.Conclusions/SignificanceThese findings suggest that in some SLE patients IFN-I dependent gene expression could be the result of a low IFNAR signaling threshold.

Endothelin-1 stimulates suppressor of cytokine signaling-3 gene expression in adipocytes

Endothelin (ET)-1 and suppressor of cytokine signaling (SOCS)-3 were respectively found to regulate energy metabolism and hormone signaling in fat cells. Although ET-1 can also regulate the expression of SOCS-3-stimulating hormones, it is still unknown whether ET-1 regulates SOCS-3 gene expression. This study investigated the pathways involved in ET-1’s modulation of SOCS-3 gene expression in 3T3-L1 adipocytes. ET-1 upregulated SOCS-3 mRNA and protein expression in dose- and time-dependent manners. The concentration of ET-1 that increased SOCS-3 mRNA levels by 250–400% was ∼100nM with 2–4h of treatment. Treatment with actinomycin D prevented ET-1-stimulated SOCS-3 mRNA expression, suggesting that the effect of ET-1 requires new mRNA synthesis. Pretreatment with the ET type A receptor (ETAR) antagonist, BQ-610, but not the ET type B receptor (ETBR) antagonist, BQ-788, prevented the stimulatory effect of ET-1 on SOCS-3 gene expression. The specific inhibitors of either MEK1 (U-0126 and PD-98059), JAK (AG-490), JNK (SP-600125), or PI3K (LY-294002 and wortmannin) reduced ET-1-increased levels of SOCS-3 mRNA and respectively inhibited ET-1-stimulated activities of MEK1, JAK, JNK, and PI3K. These results imply that the ETAR, ERK, JAK, JNK, and PI3K are functionally necessary for ET-1’s stimulation of SOCS-3 gene expression. Moreover, ET-1 was observed to upregulate expressions of SOCS-1, -2, -3, -4, -5, and -6 mRNAs, but not SOCS-7 or cytokine-inducible SH2-containing protein-1 mRNAs. This suggests that ET-1 selectively affects particular types of SOCS family members. Changes in SOCS gene expressions induced by ET-1 may help explain the mechanism by which ET-1 modulates hormone signaling of adipocytes.

Satellite Cells Derived from Obese Humans with Type 2 Diabetes and Differentiated into Myocytes In Vitro Exhibit Abnormal Response to IL-6

Obesity and type 2 diabetes are associated with chronically elevated systemic levels of IL-6, a pro-inflammatory cytokine with a role in skeletal muscle metabolism that signals through the IL-6 receptor (IL-6Rα). We hypothesized that skeletal muscle in obesity-associated type 2 diabetes develops a resistance to IL-6. By utilizing western blot analysis, we demonstrate that IL-6Rα protein was down regulated in skeletal muscle biopsies from obese persons with and without type 2 diabetes. To further investigate the status of IL-6 signaling in skeletal muscle in obesity-associated type 2 diabetes, we isolated satellite cells from skeletal muscle of people that were healthy (He), obese (Ob) or were obese and had type 2 diabetes (DM), and differentiated them in vitro into myocytes. Down-regulation of IL-6Rα was conserved in Ob myocytes. In addition, acute IL-6 administration for 30, 60 and 120 minutes, resulted in a down-regulation of IL-6Rα protein in Ob myocytes compared to both He myocytes (P<0.05) and DM myocytes (P<0.05). Interestingly, there was a strong time-dependent regulation of IL-6Rα protein in response to IL-6 (P<0.001) in He myocytes, not present in the other groups. Assessing downstream signaling, DM, but not Ob myocytes demonstrated a trend towards an increased protein phosphorylation of STAT3 in DM myocytes (P = 0.067) accompanied by a reduced SOCS3 protein induction (P<0.05), in response to IL-6 administration. Despite this loss of negative control, IL-6 failed to increase AMPKα2 activity and IL-6 mRNA expression in DM myocytes. There was no difference in fusion capacity of myocytes between cell groups. Our data suggest that negative control of IL-6 signaling is increased in myocytes in obesity, whereas a dysfunctional IL-6 signaling is established further downstream of IL-6Rα in DM myocytes, possibly representing a novel mechanism by which skeletal muscle function is compromised in type 2 diabetes.

Deficient leukemia inhibitory factor signaling in muscle precursor cells from patients with type 2 diabetes

The cytokine leukemia-inhibitory factor (LIF) is expressed by skeletal muscle and induces proliferation of muscle precursor cells, an important feature of skeletal muscle maintenance and repair. We hypothesized that muscle precursor cells from patients with type 2 diabetes had a deficient response to LIF. The mRNA and protein expressions of LIF and its receptor (LIFR) were measured in skeletal muscle biopsies from healthy individuals and patients with type 2 diabetes by use of qPCR and Western blot. LIF signaling and response were studied following administration of recombinant LIF and siRNA knockdown of suppressor of cytokine signaling (SOCS)3 in myoblast cultures established from healthy individuals and patients with type 2 diabetes. Myoblast proliferation rate was assessed by bromodeoxyuridine incorporation. LIF and LIFR proteins were increased in both muscle tissue and cultured myoblasts from diabetic patients. Nonetheless, in the diabetic myoblasts, LIF-induced phosphorylation of signal transducer and activator of transcription (STAT)1 and STAT3 was impaired. The deficient response to LIF administration in the diabetic myoblasts was further emphasized by a lack of increase in LIF-stimulated cell proliferation and a decreased LIF-stimulated induction of the proliferation-promoting factors cyclin D1, JunB, and c-myc. SOCS3 protein was upregulated in diabetic myoblasts, and knockdown of SOCS3 rescued LIF-induced gene expression in diabetic myoblasts, whereas neither STAT1 or STAT3 signaling nor proliferation rate was affected. In conclusion, although LIF and LIFR proteins were increased in muscle tissue and myoblasts from diabetic patients, LIF signaling and LIF-stimulated cell proliferation were impaired in diabetic myoblasts, suggesting a novel mechanism by which muscle function is compromised in diabetes.

MiR-155 modulates TNF-α-inhibited osteogenic differentiation by targeting SOCS1 expression

Bone morphogenetic proteins (BMPs) can induce ectopic bone formation, which is negatively regulated by inflammatory cytokines, such as tumor necrosis factor (TNF)-α. Recently, miR-155 has been reported to regulate the transforming growth factor (TGF)-β signaling pathway and inflammatory responses. However, whether and how miR-155 modulates TNF-α-regulated osteogenic differentiation have not been explored. In this study, we demonstrated that miR-155 was involved in TNF-α-mediated inhibition of osteogenic differentiation. Knockdown of miR-155 partially mitigated the inhibition of TNF-α on BMP-2-induced osteogenic differentiation. Bioinformatic analysis identified the candidate target site in the 3′ untranslated region (3′UTR) of SOCS1. Knockdown of miR-155 increased SOCS1 protein expression during TNF-α stimulation in MC3T3-E1 cells. And transfection with miR-155 inhibited the wild-type, but not the mutant, 3′UTR of SOCS1-regulated luciferase activity, indicating that SOCS1 is a direct target of miR-155 in osteoblast cells. Furthermore, miR-155 expression could be induced by TNF-α through the JNK pathway. As the result of increased SOCS1 expression, knockdown of miR-155 significantly reduced the JNK/c-Jun activation. In addition, transfection of SOCS1 siRNA or overexpression of SOCS1 coding region could narrow the differences of alkaline phosphatase (ALP) and osteocalcin (OSC) expression between the control and miR-155 inhibitor transfected cells. These data indicated that miR-155 modulates TNF-α-regulated osteogenic differentiation by targeting SOCS1, at least partially through the SAPK/JNK pathway. These findings may provide new insights into understanding the regulatory role of miR-155 in the process of osteogenic differentiation in inflammatory condition.

A novel pro-inflammatory mechanism of action of resistin in human endothelial cells: Up-regulation of SOCS3 expression through STAT3 activation

Resistin is a significant local and systemic regulatory cytokine involved in inflammation. Suppressors of cytokine signaling (SOCS) proteins are intracellular regulators of receptor signal transduction induced by several cytokines in a cytokine and cell specific manner. Resistin up-regulates SOCS3 expression in mice adipocytes but it is not known whether this is a common occurrence in other cells. We questioned whether resistin-induces SOCS3 in human endothelial cells and if signal transducer and activator of transcription (STAT) proteins are involved in the process. The Real-Time PCR and Western blot analysis showed that in resistin-activated HEC the gene and protein expression of SOCS3 were significantly increased. Furthermore, resistin induced activation of STAT3 as characterized by increased tyrosine phosphorylation. Resistin-induced SOCS3 expression was blocked by specific inhibitors of STAT3 signaling and by the transfection of siRNA specific for STAT3. Silencing of SOCS3 gene expression by transfection with SOCS3 siRNA reduced the expression of resistin induced-P-selectin and fractalkine in HEC. Together, our results demonstrate that in HEC (1) resistin up-regulates SOCS3 expression and activates STAT3 transcription factor; (2) the increase in SOCS3 mRNA and protein expression as well as STAT3 activation have a long-lasting effect (up to 18h); (3) inhibition of SOCS3 function prevents resistin-induced expression of cell adhesion molecules P-selectin and fractalkine and thus activation of endothelial cells. The data uncover a new resistin-mediated mechanism in human endothelial cells and designate SOCS3 as a novel therapeutic target to modulate resistin-dependent inflammation in vessel wall diseases.

Expression of SOCS1 and SOCS3 Is Altered in the Nasal Mucosa of Patients with Mild and Moderate/Severe Persistent Allergic Rhinitis

Background: The aim of this study was to evaluate the role of suppressor of cytokine signaling (SOCS) molecules, SOCS1 and SOCS3, which act as negative regulators of cytokine signaling in various allergic diseases, in patients with mild and moderate/severe persistent allergic rhinitis. Methods: The expression and distribution pattern of SOCS1 and SOCS3 were analyzed in nasal mucosa and peripheral blood mononuclear cells (PBMC) of healthy controls, and patients with mild and moderate/severe persistent allergic rhinitis using RT-PCR, immunohistochemistry and Western blotting. IL-4, IL-13, IL-15 and IFN-γ expression was also analyzed in the nasal mucosa of each individual using RT-PCR and Western blotting. Results: SOCS1 and SOCS3 mRNA and protein expression was significantly increased in the nasal mucosa and PBMC of patients with mild and moderate/severe persistent allergic rhinitis compared with healthy controls. In healthy and allergic nasal mucosa, they were commonly localized to the epithelium, submucosal glands and endothelium, showing stronger staining intensity in mild and moderate/severe persistent allergic nasal mucosa than in healthy nasal mucosa. Tissue levels of IL-4 and IL-13 were increased in moderate/severe persistent allergic nasal mucosa whereas IL-15 and IFN-γ were decreased in moderate/severe persistent allergic nasal mucosa. Conclusions: Upregulation of SOCS1 and SOCS3 in mild and moderate/severe persistent allergic rhinitis suggests that SOCS proteins may be important regulators in the pathogenesis of allergic rhinitis and play a role as molecular determinants of allergic rhinitis persistence.

α(1,3)‐Fucosylation alters STAT3‐dependent IL‐17 production in vivo

Mice deficient in α(1,3)‐fucosyltransferase (FucT)‐IV and ‐VII (DKO) lack selectin ligand activity, have severe deficiencies in leukocyte trafficking, and have a marked increase in circulating IL‐ 17a compared to wild‐type (WT) mice. We sought to determine how the loss of FucT‐IV/‐VII activity alters the intracellular signaling cascade responsible for IL‐17a induction. Mononuclear leukocytes were isolated from the spleen of WT and DKO mice. Messenger RNA was isolated and converted to cDNA. qPCR was performed using Sybr green‐based detection and standardized to B‐actin. DKO mice have elevated transcript levels of RORγT and IL‐17a (18‐fold and 30‐fold, respectively) compared to WT, and reduced levels of STAT3 and SOCS3 transcript (5‐fold and 6‐fold, respectively). Protein for western blots was isolated from the whole spleen of 12 week old male mice, separated on a 10% polyacrylamide gel, transferred to a 0.22 μm nitrocellulose membrane and probed with antibodies to SOCS3, RORγT, STAT3, or γ‐Tubulin. DKO mice have drastically reduced levels of STAT3 and SOCS3 protein and increased levels of RORγT protein compared to WT mice. These data show that loss of FucT‐IV and ‐ VII activity alters the STAT3 signaling cascade thought to be solely responsible for IL‐17a induction. They suggest that loss of FucT‐IV and ‐VII activity may allow an alternate signaling pathway to drive IL‐17a production independent of STAT3.

Expression of constitutively active Jak2 in the hypothalamus leads to weight gain that correlates with increased SOCS3 levels

The leptin pathway is of great clinical interest for weight loss. However, intricate feedback signals obscure viable strategies to affect leptin‐mediated weight loss. We aim to understand this pathway and determine if a constitutively active positive regulator of leptin signaling, Jak2 V617F, alters weight gain and energy intake.Hypothalamic injection of pLentiV617F and pLenti‐GFP was carried out. Rats were given high fat diet and monitored for food intake/weight changes. Oxygen consumption and fat pad analysis was conducted. After tissue extraction QPCR was used to verify expression of transgenes and evaluate levels of endogenous Jak2 transcript and immunoblot to measure Jak2 and SOCS3 protein.Body weight, intake and food efficiency for the V617F rats was up. Concordantly, respiration and voluntary wheel running activity was down. Transgene expression was elevated, as expected, along with leptin and hypothalamic SOCS3 protein in V617F‐injected rats.V617F is indicated to cause caloric increase and metabolic decrease. SOCS3 was up, indicating induction of an inhibitory pathway. We suspect this obese phenotype is caused by an inhibition of Jak2 signaling by SOCS3 in the hypothalamus. This delicate balance between Jak2 expression and metabolic/energy intake regulation and stands as a cautionary tale for pharmacologists who choose to alter these proteins by pharmacological means.