Suppressors Of Cytokine Signaling Expression Research Articles

Identification of the Prognostic Value Among Suppressor Of Cytokine Signaling Family Members in Kidney Renal Clear Cell Carcinoma.

Background: Kidney renal clear cell carcinoma (KIRC) has become one of the most prevalent malignancies worldwide and remains a crucial cause of cancer-related morbidity and mortality. Aberrant activation of the JAK/STAT pathway acts as an important role in KIRC. The suppressor of cytokine signaling (SOCS) family members are the key negative regulators of the JAK/STAT pathway. SOCS family members have been verified to act as significant roles in regulating cellular responses to many cytokines and growth factors. However, whether the expression levels of SOCS affect the prognosis of patients with KIRC is still elusive. Methods: We first evaluated the expression of SOCS family genes in KIRC and determined the correlation between SOCS expression and different clinicopathological features. Then, we analyzed the genetic alterations, potential functions, transcription factor targets, and immune infiltration of SOCS family members based on the information available on public databases. Finally, we assessed the prognostic value of differentially expressed SOCS family members. Results: The expression levels of SOCS2, SOCS4, SOCS6, SOCS7, and CISH were downregulated in KIRC, and all SOCS genes were associated with clinicopathological features of patients with KIRC. SOCS family members have been predominantly related to protein binding, signaling adaptor activity, and JAK/STAT cascade. We found that STAT3, STAT6, and IRF1 are the key transcription factors that may be participated in the regulation of SOCS. We also found an association between the expression levels of SOCS and the immune infiltrates of KIRC. Finally, we have illuminated that SOCS1 and SOCS3 are risky genes, whereas SOCS2, SOCS4, SOCS6, SOCS7, and CISH are some of the protective genes for patients with KIRC; based on these, we have created a KIRC prognostic index for predicting the prognosis of patients of KIRC. Conclusion: Our study may contribute to further understanding the functions of SOCS genes in KIRC, which may help clinicians in selecting the appropriate drugs and predicting the outcomes for patients with KIRC.

IL-17A Attenuates IFN-λ Expression by Inducing Suppressor of Cytokine Signaling Expression in Airway Epithelium.

IFN-λ is a cytokine expressed in epithelial tissues and plays a central role in antiviral mucosal immune response. The expression of IFN-λ in the airway is impaired in chronic airway diseases (e.g., asthma, chronic obstructive pulmonary disease), which renders patients susceptible to viral infection. IL-17A is associated with asthma and chronic obstructive pulmonary disease pathogenesis; however, IL-17A regulation of IFN-λ expression remains unclear. The aim of the current study is to clarify IL-17A-mediated regulatory mechanisms of IFN-λ expression in human airway epithelial cells. In this study, we have shown that polyinosinic:polycytidylic acid (polyI:C) and influenza A virus (IAV) infection increased IFN-λ expression at mRNA and protein levels in primary cultures of normal human bronchial epithelial cells, whereas IL-17A attenuated polyI:C- or IAV-induced IFN-λ expression. IFN-λ receptor 1 knockdown and a JAK inhibitor, ruxolitinib, attenuated polyI:C-induced IFN-λ expression, confirming that a positive autocrine feedback loop, the IFN-λ receptor-JAK-STAT pathway, was involved in IFN-λ expression. In Western blotting analysis, we demonstrated that polyI:C and IAV infection induced STAT1 phosphorylation in normal human bronchial epithelial cells, whereas IL-17A suppressed polyI:C- or IAV-mediated STAT1 phosphorylation. Furthermore, we found that cotreatment with IL-17A and polyI:C or IAV infection synergistically increased suppressor of cytokine signaling (SOCS)1 and SOCS3 expression. SOCS1 small interfering RNA and SOCS3 small interfering RNA negated the inhibitory effect of IL-17A in polyI:C-induced IFN-λ expression by restoring attenuated STAT1 phosphorylation. Taken together, these findings indicate that IL-17A attenuates virus-induced IFN-λ expression by enhancing SOCS1 and SOCS3 expression to inhibit autocrine signaling loops in human airway epithelial cells.

Hijack and exploitation of host SOCS proteins: An immunosuppressive deception of the viruses

The suppressors of cytokine signaling (SOCS) are a cytoplasmic protein family that completes a negative feedback loop to attenuate signal transduction from cytokines through the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway. They work as a natural precaution to pre-vent excessive immune responses that could cause collateral damage to body tissues. But viruses use SOCS proteins to suppress the proportionate immune response also so that a vulnerable environment can be developed in host body to let them grow freely. In several cases, an increased expression of SOCS proteins has been reported in virus infected individuals, which is believed to be induced by the viruses to inhibit the anti-proliferative and antiviral activity of cytokines (Interferon) of host body. Viruses including HIV hijack the expression of SOCS proteins and manipulate them in a way where they support the onset of antigens in host body by suppressing the cell sig-nalling of immune response. Detailed mechanism of the same and an alter-native way to stop viral infection by restoring the normal SOCS expression is discussed in the present review.

Endotoxin tolerance and cross-tolerance in mast cells involves TLR4, TLR2 and FcεR1 interactions and SOCS expression: perspectives on immunomodulation in infectious and allergic diseases

BackgroundThe study of the endotoxin tolerance phenomenon in light of the recently defined roles of mast cells and toll-like receptors as essential components of the innate immune response and as orchestrators of acquired immunity may reveal potentially useful mechanisms of immunomodulation of infectious and allergic inflammatory responses, such as sepsis or asthma. Here we evaluated the phenomenon of direct tolerance of endotoxins, as well as the induction of cross-tolerance and synergism by stimulation with toll-like receptor-2 (TLR2) and FcεR1 agonists, in murine mast cells prestimulated with lipopolysaccharide (LPS). Additionally, we evaluated some stimulatory and inhibitory signaling molecules potentially involved in these phenomena.MethodsMC/9 cells and primary bone marrow-derived mast cells obtained from C57BL/6 and TLR4-/- knock-out mice were sensitized to DNP-HSA (antigen) by incubation with DNP-IgE and were prestimulated with LPS for 18 hr prior to stimulation. Cultures were stimulated with LPS or Pam3Cys-Ser-(Lys)4 3HCl (P3C), a TLR2 agonist, individually or in combination with antigen. The production of IL-6 and TNFα, the phosphorylation of NFκB and p38 MAPK, and the expression of TLR4 and SOCS-1 and -3 were analyzed.ResultsWe found that production of TNFα and IL-6 in murine mast cells that have been pretreated with LPS and challenged with TLR4 (LPS) or -2 (P3C) agonists was reduced, phenomena described as endotoxin tolerance (LPS) and cross-tolerance (P3C), respectively. The expression of TLR4 was not affected by LPS pretreatment. Our results show that the FcεR1 agonist DNP-HSA (antigen) interacts synergistically with LPS or P3C to markedly enhance production of cytokines (TNFα and IL-6). This synergistic effect with LPS and P3C was also attenuated by LPS pretreatment and was mediated by TLR4. These results may be attributed to the reduction in phosphorylation of the mitogen-activated protein kinase (MAPK), p38, and the transcription factor NFκB, as well as to an increase in the expression of the suppressors of cytokine signaling (SOCS)-1 and -3 proteins in LPS-pretreated mast cells.ConclusionsThese findings can be explored with respect to the modulation of inflammatory responses associated with infectious and allergic processes in future studies.

MicroRNA‐98 andlet‐7Regulate Expression of Suppressor of Cytokine Signaling 4 in Biliary Epithelial Cells in Response toCryptosporidium parvumInfection

Expression of the cytokine-inducible Src homology 2 (CIS) protein and suppressors of cytokine signaling (SOCS) proteins represents an important element of host cell reactions in response to infection. We have demonstrated previously that Cryptosporidium parvum infection down-regulates microRNA-98 (miR-98) and let-7 to induce CIS expression in biliary epithelial cells. We report here that down-regulation of miR-98 and let-7 also coordinates epithelial expression of SOCS4 after C. parvum infection. Targeting of the SOCS4 3' untranslated region by miR-98 or let-7 resulted in translational repression. Functional manipulation of miR-98 caused reciprocal alterations in SOCS4 protein expression. Transfection of miR-98 precursor abolished C. parvum-stimulated SOCS4 up-regulation. Moreover, expression of SOCS4 in epithelial cells showed an inhibitory effect on phosphorylation of signal transducers and activators of transcription proteins induced by C. parvum. These data suggest that miRNAs play an important role in the coordinated regulation of CIS and SOCS expression in epithelial cells in response to C. parvum infection.

Pro-inflammatory Cytokines Induce Suppressor of Cytokine Signaling-3 in Human Periodontal Ligament Cells

Introduction Periapical inflammation is initiated by insult to the dental pulp and mediated by inflammatory cytokines in the periodontal tissue. On the other hand, the destruction of tissue can be prevented by the suppression of pro-inflammatory cytokine activity. The balance between these cytokines and their counterregulatory molecules has been suggested to regulate tissue destruction. Suppressors of cytokine signaling (SOCS) proteins are known to suppress inflammatory cytokine signaling via the classic negative feedback loop. However, the mechanism by which they are induced by inflammatory cytokines and regulated during the development of periodontal disease remains to be clarified. We investigated the effects of inflammatory cytokines on SOCS protein expression and their signaling pathways in human periodontal ligament (PDL) cells. Methods We examined the effect of inflammatory cytokines on SOCSs expression and its signaling pathway in human PDL cells using reverse transcription- and real-time polymerase chain reaction, Western blot methods. Furthermore, we also examined whether these cytokines-induced SOCS-3 suppress chemokines secretion using ELISA methods. Results We found that inflammatory cytokines interleukin (IL)-1β and IL-6 induced expression of SOCS-3 but not that of SOCS-2 in human PDL cells. IL-1β and IL-6 simultaneously induced IL-8 and monocyte chemoattractant protein-1 secretion in PDL cells, whereas SOCS-3 overexpression suppressed secretion of these chemokines through inhibition of phosphorylation in downstream signaling. Conclusion The results suggest that pro-inflammatory cytokines induced SOCS-3 expression. The SOCS-3 induction suggests playing an important role in negative feedback, suppressing serious destruction of periodontal tissue in apical periodontitis through a chemokine-dependent mechanism.

High glucose induces suppression of insulin signalling and apoptosis via upregulation of endogenous IL-1β and suppressor of cytokine signalling-1 in mouse pancreatic beta cells

Chronic hyperglycemia and inflammatory cytokines disrupt and/or attenuate signal transduction pathways that promote normal β-cell survival, leading to the destruction of endocrine pancreas in type 2 diabetes. There is convincing evidence that autocrine insulin signalling exerts protective anti-apoptotic effects on beta cells. Suppressors of cytokine signalling (SOCS) were induced by several cytokines and inhibit insulin-initiated signal transduction. The aim of this study was to investigate whether high glucose can influence endogenous interleukin-1β (IL-1β) and SOCS expression thus affecting insulin signalling and survival in insulin-producing mouse pancreatic beta cells (βTC-6). Results showed that prolonged exposure of βTC-6 cells to increased glucose concentrations resulted in significant inhibition of insulin-induced tyrosine phosphorylation of the insulin receptor (IR), and insulin receptor substrate-2 (IRS-2) as well as PI3-kinase activation. These changes were accompanied by impaired activation of the anti-apoptotic signalling protein Akt and annulment of Akt-mediated suppression of the Forkhead family of transcription factors (FoxO) activation. Glucose-induced attenuation of IRS-2/Akt-mediated signalling was associated with increased IL-1β expression. Enhanced endogenous IL-1β specifically induced mRNA and protein expression of SOCS-1 in βTC-6 cells. Inhibition of SOCS-1 expression by SOCS-1-specific small interfering RNA restored IRS-2/PI3K-mediated Akt phosphorylation suppressed by high glucose. The upregulation of endogenous cytokine signalling and FoxO activation were accompanied by enhanced caspase-3 activation and increased susceptibility of cells to apoptosis. These results indicated that glucose-induced endogenous IL-1β expression increased βTC-6 cells apoptosis by inhibiting, at least in part, IRS-2/Akt-mediated signalling through SOCS-1 upregulation.

MCP-1 (Monocyte Chemotactic Protein-1)-induced Protein, a Recently Identified Zinc Finger Protein, Induces Adipogenesis in 3T3-L1 Pre-adipocytes without Peroxisome Proliferator-activated Receptor γ

Adipogenesis is a key differentiation process relevant to obesity and associated diseases such as type 2 diabetes. This process involves temporally regulated genes controlled by a set of transcription factors, CCAAT/enhancer-binding proteins (C/EBP) beta, C/EBPdelta, and C/EBPalpha and peroxisome proliferator-activated receptor gamma (PPARgamma). Currently, PPARgamma is universally accepted as the master regulator that is necessary and sufficient to induce adipogenesis as no known factor can induce adipogenesis without PPARgamma. We present evidence that a novel zinc finger protein, MCP-1-induced protein (MCPIP), can induce adipogenesis without PPARgamma. Classical adipogenesis-inducing medium induces MCP-1 production and expression of MCPIP in 3T3-L1 cells before the induction of the C/EBP family of transcription factors and PPARgamma. Knockdown of MCPIP prevents their expression and adipogenesis as measured by expression of adipocyte markers and lipid droplet accumulation. Treatment of 3T3-L1 cells with MCP-1 or forced expression of MCPIP induces expression of C/EBPbeta, C/EBPdelta, C/EBPalpha, and PPARgamma and adipogenesis without any other inducer. Forced expression of MCPIP induces expression of the C/EBP family of transcription factors and adipogenesis in PPARgamma(-/-) mouse embryonic fibroblasts. Thus, MCPIP is a newly identified protein that can induce adipogenesis without PPARgamma.

Prognostic relevance of 9q34 deletion and the suppressor of cytokine signalling-1 in CML patients

Chronic myeloid leukemia (CML) is characterized by formation of the BCR/ABL fusion gene. The response to therapy may vary because of development of secondary cytogenetic changes or resistance. In addition, suppressor of cytokine signalling (SOCS) proteins is also hypothesized as a cause of resistance and poor prognosis when aberrantly overexpressed. This study aims to determine the incidence and prognostic value of the 9q34 deletion using fluorescence in situ hybridization and SOCS-1 mRNA aberrant expression by PCR in 43 CML patients at different phases of the disease and in 10 normal controls and correlate the data to interferon response. All patients were Philadelphia-positive, deletions of 9q34 were observed in 20.9% of all patients (13.3% chronic phase, 10% accelerated phase and 33.3% in blast crisis). SOCS expressions were positive in 53.4% of all patients (40% chronic phase, 50% AP and 66.67% in blast crisis). Analysing outcome based on 9q34 deletion and SOCS expression status showed a statistically significant difference in overall survival and progression-free survival between those with deletions and those without (P<0.001) and between those with abnormal SOCS expression and those without (P<0.001). Deletion of 9q34 and aberrant expression of SOCS-1 are associated with poor prognosis in CML patients with different phases of the disease under interferon therapy.

Increased SOCS expression in peripheral blood mononuclear cells of end stage renal disease patients is related to inflammation and dialysis modality

Inflammation is a characteristic of cardiovascular disease and is increased in end-stage renal disease. Suppressors of cytokine signaling (SOCS) inhibit and reflect activation of intracellular inflammatory pathways. We hypothesized that SOCS expression in peripheral blood mononuclear cells of end stage renal disease patients is increased. Whether SOCS expression in peripheral blood mononuclear cells is related to inflammation, dialysis, and dialysis modality was investigated. Monocytes and lymphocytes were isolated from peripheral blood mononuclear cells of patients not on dialysis ( n = 8), on peritoneal dialysis ( n = 8), on hemodialysis ( n = 14) and of healthy control ( n = 15) subjects. SOCS expression was assessed by real-time quantitative PCR and plasma cytokines by ELISA. In end stage renal disease patients monocyte SOCS1, and lymphocyte SOCS1 and cytokine-inducible SH2 containing protein-1 (CIS-1) gene expression were increased along with increased plasma levels of interleukin (IL)-6, tumor necrosis factor (TNF)α ,and C-reactive protein (CRP). Monocyte SOCS1 correlated with IL-6. Lymphocyte CIS-1 was increased in non-dialysis and peritoneal dialysis but not in hemodialysis patients. Lymphocyte CIS-1 in peritoneal dialysis patients correlated with plasma TNFα. Despite the relatively low number of patients studied we observed increased expression of SOCS1 in both monocytes and lymphocytes, and of CIS-1 solely in lymphocytes of the patients. SOCS expression was related to increased systemic inflammation, illustrated by a significant correlation between monocyte SOCS1 and plasma IL-6. SOCS expression in peripheral blood mononuclear cells was also affected by hemodialysis, indicated by increased lymphocyte CIS-1 in non-dialysis and peritoneal dialysis but not in hemodialysis patients. We suggest that increased SOCS expression in peripheral blood mononuclear cells of end stage renal disease patients reflects whether and to which extent systemic inflammation activates the intracellular inflammatory pathways.

Targeting Growth Factors in Arthritis: A Rational for Restoring the IGF-I Response in Chondrocytes

The role of growth factors in the pathogenesis of arthritis has received considerably less attention as compared to proinflammatory cytokines in recent years. This is understandable as it is evident that current anti-tumor necrosis factor-α (TNFα) therapy is efficacious in at least in 60% of the rheumatoid arthritis (RA) patients and when given in combination with methotrexate stops radiological progression of bone erosion. Other proinflammatory cytokines, such as interleukin-1 (IL-1) and IL-17 have also been implicated in the dysregulation of bone and cartilage remodelling characteristic of rheumatoid arthritis (RA) and/or osteoarthritis (OA). The direct effects of anti-cytokine treatment on cartilage pathology are not that easy to determine in humans and it remains to be seen if amelioration of cartilage destruction or better cartilage repair has been accomplished with anti-TNF therapy. A complicating factor is that chondrocytes in RA and OA become non-responsive to insulin-like growth factor-I (IGF-I). IGF-I is the main growth factor for stimulation of chondrocyte proteoglycan and collagen type II synthesis in order to maintain the cartilage matrix integrity. This article reviews our current understanding of the role of IGF-I on cartilage extracellular matrix production and the mechanisms underlying the cause of IGF-I non-responsiveness, and in particular the inhibition of IGF-receptor signalling by suppressor of cytokine signalling (SOCS) proteins. The epigenetic and cytokine-dependent regulation of SOCS expression may give an explanation for the loss of IGF-I signalling in chondrocytes in ageing-related diseases such as OA and RA. Whether IGF-1 is replaceable by other growth factors to maintain the cartilage extracellular matrix will be discussed. It is concluded that in addition to the current use of anti-cytokine therapy in arthritis the IGF-I response of chondrocytes must be restored in order to achieve cartilage matrix repair.

CCL11 blocks IL-4 and GM-CSF signaling in hematopoietic cells and hinders dendritic cell differentiation via suppressor of cytokine signaling expression

The chemokine eotaxin/CCL11 is an important mediator of leukocyte migration, but its effect on inflammatory cytokine signaling has not been explored. In this study, we find that CCL11 induces suppressor of cytokine signaling (SOCS)1 and SOCS3 expression in murine macrophages, human monocytes, and dendritic cells (DCs). We also discover that CCL11 inhibits GM-CSF-mediated STAT5 activation and IL-4-induced STAT6 activation in a range of hematopoietic cells. This blockade of cytokine signaling by CCL11 results in reduced differentiation and endocytic ability of DCs, implicating CCL11-induced SOCS as mediators of chemotactic inflammatory control. These findings demonstrate cross-talk between chemokine and cytokine responses, suggesting that myeloid cells tracking to the inflammatory site do not differentiate in the presence of this chemokine, revealing another role for SOCS in inflammatory regulation.

Suppressor of cytokine signaling expression with increasing severity of murine hepatic ischemia-reperfusion injury

Preservation of function requires tight regulation of the cellular events initiated when hepatic ischemia is followed by reperfusion (IR). One important mechanism modulating the cytokine-directed response to injury is Suppressors of Cytokine Signaling. SOCS1 and SOCS3 ensure appropriate intensity and duration of cytokine signaling through negative feedback on JAK-STAT signaling. The contribution of SOCS1 and SOCS3-mediated regulation to the evolution of hepatic IR injury is unknown. C57Blk6 mice were subjected to mild (20 min) or severe (90 min) hepatic ischemia. Liver was analyzed for cytokine and SOCS1/3 induction as well as JAK-STAT activation at intervals after reperfusion. Tnf, Il-1beta, and Il-6 expression paralleled increasing injury severity. Despite early phosphorylation of both STAT1 and STAT3 after severe injury, only nuclear translocation of activated STAT3, suggesting that the induction of target genes through JAK-STAT after IR is predominantly via STAT3. Socs3 was expressed across the injury spectrum while Socs1 was induced only in the face of severe IR injury. Severe IR in Il-6 deficient mice confirmed that Il-6, acting via STAT3, serves as a primary inducer of both regulatory mechanisms. Under the influence of IL-6-mediated STAT3 signaling, Socs1 serves as a complimentary regulatory mechanism when Socs3 is insufficient to limit cytokine-mediated inflammation after hepatic IR.

Effect of Intranasal vs. Intraperitoneal Sensitization of Mice with House Dust Mite Antigen on Airway Hyperresponsiveness (AHR) and SOCS expression in the Lung

Increased density of Th2 cells with the secretion of IL-4, IL-5, IL-9, and IL-13 in the airways are hallmarks of allergic asthma, and induce AHR, airway inflammation, mucus hypersecretion, and goblet cell hyperplasia. These cytokines are modulated by a family of proteins called suppressor of cytokine signaling (SOCS). In this study, we investigated whether or not the route of sensitization with house dust mite induces different effects on the development of AHR and on SOCS expression in the lungs. Mice were sensitized either by intranasal injection (IN) or by intraperiotneal injection (IP) with house dust mite antigen (10 μg). Alum was used as an adjuvant only in IP sensitization. AHR to methacholine was determined by BUXCO. Staining of the lungs with H&E and tri-chrome was used to compare morphology and collagen deposition, respectively. Periodic Acid Schiff (PAS) staining was done to visualize goblet cell hyperplasia and mucus deposition and immunohistochemistry (IHC) was performed to visualize the expression of SOCS 1, 3, and 5. IN route of antigen sensitization induced a significantly increased AHR, airway inflammation, goblet cell hyperplasia, collagen deposition, and expression of SOCS1, 3, and 5 in the mouse lung compared to the IP route of antigen administration. Intranasal administration of the house dust mite antigen causes significantly increased induction of allergic airway response than by intraperitoneal route. This could serve as a better model to investigate the effects of potential therapeutic agents in allergic asthma.

IL-4 and IL-13 Negatively Regulate TNF-α- and IFN-γ-Induced β-Defensin Expression through STAT-6, Suppressor of Cytokine Signaling (SOCS)-1, and SOCS-3

Human beta-defensins (HBDs) are a major class of antimicrobial peptides that play an important role in the innate immune response, however, the induction and regulation of these antimicrobial peptides is not well understood. We demonstrate here that stimulation of keratinocytes with TNF-alpha/IFN-gamma induces HBD-2 and HBD-3 by activating STAT-1 and NF-kappaB signaling. We further demonstrate that IL-4 and IL-13 activate STAT-6 and induce the suppressors of cytokine signaling (SOCS)-1 and -3. This interferes with STAT-1 and NF-kappaB signaling, thereby inhibiting TNF-alpha/IFN-gamma-mediated induction of HBD-2 and HBD-3. These data suggest that targeting the STAT-1-signaling pathway or suppressor of cytokine signaling expression enhances beta-defensin expression and represents a new therapeutic strategy for reduction of infection in human diseases associated with beta-defensin deficiency.

Development of IFN-γ resistance is associated with attenuation of SOCS genes induction and constitutive expression of SOCS 3 in melanoma cells

The resistance to interferons (IFNs) limits their anticancer therapeutic efficacy. Here we studied the evolution of an IFN-resistant state in vitro using melanoma cell lines. We found that the cells became less sensitive to antiproliferative effect of IFN-γ after prolonged cultivation enabling us to isolate sensitive and resistant subclones of the parental line. We investigated transcription of signal transducer and activator of transcription (STAT) 1–6 and suppressor of cytokine signalling (SOCS) 1–3 genes, and phosphorylation of STAT 1 protein. The resistant subline (termed WM 1158R) differed from the sensitive subline (WM 1158S) by a constitutive expression of SOCS 3, lack or weak SOCS 1–3 activation following IFN-γ, and short duration of cytokine activatory signal. Similar correlations were observed in additional melanoma lines differing in IFN sensitivities. At the protein level, IFN-γ induced strong and prolonged STAT 1 activation at serine 727 (S727) in WM 1158R while in WM 1158S cells phosphorylation of this amino acid was much less pronounced. On the other hand, phosphorylation of tyrosine 701 (Y701) was stimulated regardless of the sensitivity phenotype. In conclusion, constitutive expression of SOCS 3 is correlated with attenuation of its induction following IFN treatment. These results suggest that progression of melanoma cells from IFN sensitivity to IFN insensitivity associates with changes in SOCS expression.

Hepatic growth hormone resistance during sepsis is associated with increased suppressors of cytokine signaling expression and impaired growth hormone signaling

During sepsis, a two- to four-fold increase in circulating growth hormone (GH) is seen with 40-50% reductions in plasma insulin-like growth factor (IGF)-I. The suppressors of cytokine signaling (SOCS), inhibitors of cytokine, and growth factor signaling via the janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway have been implicated in the development of hepatic GH resistance. In this study we examine the effects of sepsis on GH-induced IGF-I expression and potential mechanisms for GH resistance. Prospective experimental study. University research laboratory. Male Sprague-Dawley rats. Rats were randomized to laparotomy alone (control) or implantation of fecal agar pellets inoculated with Escherichia coli and Bacteroides fragilis (sepsis). GH was injected intravenously to assess hepatic IGF-I synthesis and GH signaling. Plasma IGF-I was measured in both groups at baseline (4 hrs postoperatively) and then again at 12 hrs and 24 hrs after GH administration. Basal IGF-I levels were similar in both groups, but controls had a 35% increase in IGF-I at 12 hrs, whereas septic rats demonstrated reductions in circulating IGF-I at 12 and 24 hrs after GH. Hepatic expression of SOCS-1, -2, -3, and cytokine-inducible SH2-containing protein (CIS) were determined at 1, 4, 8, and 24 hrs in septic and control rats by Northern blot. SOCS-1, SOCS-3, and CIS messenger RNA in liver were increased from 4 to 8 hrs after the induction of sepsis (p < .05 for SOCS-1 and -3). Total GH receptor (GHR), JAK2, and STAT5 signaling proteins and the time course of STAT5 activation were also measured in liver after recombinant human GH administration by immunoblot and electrophoretic mobility shift analysis. Levels of total GHR, JAK2, and STAT5 were unaltered in liver from septic rats. However, phosphorylated STAT5 and STAT5 DNA binding were significantly reduced 30 mins after GH administration in liver from septic rats. Sepsis diminished STAT5 phosphorylation and activity in liver as well as plasma IGF-I following GH administration. Hepatic messenger RNA expression of SOCS-1, SOCS-3, and CIS was transiently increased during abdominal sepsis and temporally associated with the development of hepatic GH resistance.

Induction of suppressors of cytokine signaling (SOCS) in the retina during experimental autoimmune uveitis (EAU): Potential neuroprotective role of SOCS proteins

Suppressors of cytokine signaling (SOCS) are implicated in immunopathogenic mechanisms of autoimmune diseases. We show here that SOCS expression in retina is temporarily correlated with progression of experimental autoimmune uveitis (EAU), an organ-specific autoimmune disease that serves as model of human uveitis. Peak of EAU correlates with highest SOCS genes expression while disease resolution coincides with their down-regulation. Surprisingly, SOCS5 is constitutively expressed in retina. SOCS5 expression increases significantly during EAU and remains elevated even after disease resolution. Our data suggest that cytokine-inducible SOCS members may be involved in negative regulation of inflammatory cytokines activities during EAU, while constitutively expressed SOCS5 may have neuroprotective functions.

Interferon-gamma produced by encephalitogenic cells induces suppressors of cytokine signaling in primary murine astrocytes

Suppressors of cytokine signaling (SOCS) are proteins that modulate cytokine responses in lymphoid cells. In these studies, cultured primary mouse astrocytes expressed SOCS-3 mRNA constitutively. Treatment with interferon-gamma (IFN-g) induced SOCS-1 and enhanced SOCS-3 expression, and was associated with decreased tumor necrosis factor-alpha (TNF) and increased leukemia inhibitory factor (LIF) in culture supernatants. Treatment with conditioned medium from myelin basic protein-stimulated encephalitogenic lymphoid cells (MBP-CM) increased SOCS-3 and induced SOCS-1 expression. The effects were largely due to IFN-g in MBP-CM, as anti-IFN-g antibody diminished induction. These findings suggest a role for IFN-g-induced SOCS expression in regulation of CNS inflammatory responses by astrocytes.

Activation of STAT signaling pathways and induction of suppressors of cytokine signaling (SOCS) proteins in mammalian lens by growth factors.

This study was conducted to examine whether the effects of growth factors are mediated in the lens by Janus kinase/signal transducers and activators of transcription (JAK/STAT) pathways and whether they induce expression of suppressors of cytokine signaling (SOCS), a novel family of feedback regulators of cytokine and growth factor activities. STAT activation and SOCS expression were analyzed in transgenic or wild-type mouse lens and lens epithelial cells stimulated with growth factors by immunohistochemistry, RT-PCR, Northern, Western, proliferation, or transient reporter assays. STATs were constitutively expressed at low levels and activated by insulin-like growth factor (IGF)-1, platelet-derived growth factor (PDGF)-aa, and FGF-1 or -2 in the lens. The Intensity of STAT signaling increased at high FGF-2 concentration and FGFs act in synergy with IGF-1 or PDGFaa to enhance STAT signaling and SOCS expression. Growth factor-induced proliferation of lens cells is inhibited by AG-490, a specific inhibitor of JAK2/STAT3. This is the first report that FGFs activate STAT pathways in the lens and that SOCS proteins are constitutively expressed and upregulated by growth factors in this tissue. Physiological relevance of STAT pathways in the lens is underscored by inhibition of lens cell proliferation by inhibitors of JAK/STAT pathways and by the aberrant proliferation of lens epithelium in the posterior pole of transgenic mice with constitutively activated STAT1 in the lens. Common activation of STAT pathways by FGF-1, FGF-2, IGF-1, or PDGFaa and their synergistic activation of STATs and SOCS in lens cells suggest that activities and crosstalk between these factors are sensitive to the steady state levels of activated STATs in the lens and may be under feedback regulation by SOCS family proteins.