Negative regulation of cytokine signaling by the SOCS proteins

A de novo transcriptome analysis shows that modulation of the JAK-STAT signaling pathway by salmonid alphavirus subtype 3 favors virus replication in macrophage/dendritic-like TO-cells

BACKGROUND

The Janus kinase (Jak) and signaling transducer activator of transcription (Stat) pathway mediates the signaling of genes required for cellular development and homeostasis. To elucidate the effect of type I IFN on the Jak/stat pathway in salmonid alphavirus subtype 3 (SAV3) infected macrophage/dendritic like TO-cells derived from Atlantic salmon (Salmo salar L) headkidney leukocytes, we used a differential transcriptome analysis by RNA-seq and the Kyoto encyclopedia of genes and genomes (KEGGs) pathway analysis to generate a repertoire of de novo assembled genes from type I IFN treated and non-treated TO-cells infected with SAV3.

RESULTS

Concurrent SAV3 infection with type I IFN treatment of TO-cells suppressed SAV3 structural protein (SP) expression by 2log10 at 2 days post infection compared to SAV3 infection without IFN treatment which paved way to evaluating the impact of type I IFN on expression of Jak/stat pathway genes in SAV3 infected TO-cells. In the absence of type I IFN treatment, SAV3 downregulated several Jak/stat pathway genes that included type I and II receptor genes, Jak2, tyrosine kinase 2 (Tyk2), Stat3 and Stat5 pointing to possible failure to activate the Jak/stat signaling pathway and inhibition of signal transducers caused by SAV3 infection. Although the suppressor of cytokine signaling (SOCS) genes 1 and 3 were upregulated in the IFN treated cells, only SOCS3 was downregulated in the SAV3 infected cells which points to inhibition of SOCS3 by SAV3 infection in TO-cells.

CONCLUSION

Data presented in this study shows that SAV3 infection downregulates several genes of the Jak/stat pathway, which could be an immune evasion strategy, used to block the transcription of antiviral genes that would interfere with SAV3 replication in TO-cells. Overall, we have shown that combining de novo assembly with pathway based transcriptome analyses provides a contextual approach to understanding the molecular networks of genes that form the Jak/stat pathway in TO-cells infected by SAV3.

The role of suppressors of cytokine signalling in human neoplasms

Suppressors of cytokine signalling 1-7 (SOCS1-7) and cytokine-inducible SH2-containing protein (CIS) are a group of intracellular proteins that are well known as JAK-STAT and several other signalling pathways negative feedback regulators. More recently several members have been identified as tumour suppressors and dysregulation of their biological roles in controlling cytokine and growth factor signalling may contribute to the development of many solid organ and haematological malignancies. This review explores their biological functions and their possible tumour suppressing role in human neoplasms.

Regulation of hepatocyte fate by interferon-γ

Interferon (IFN)-γ is a cytokine known for its immunomodulatory and anti-proliferative action. In the liver, IFN-γ can induce hepatocyte apoptosis or inhibit hepatocyte cell cycle progression. This article reviews recent mechanistic reports that describe how IFN-γ may direct the fate of hepatocytes either towards apoptosis or a cell cycle arrest. This review also describes a probable role for IFN-γ in modulating hepatocyte fate during liver regeneration, transplantation, hepatitis, fibrosis and hepatocellular carcinoma, and highlights promising areas of research that may lead to the development of IFN-γ as a therapy to enhance recovery from liver disease.

RSV replication is attenuated by counteracting expression of the suppressor of cytokine signaling (SOCS) molecules

Human RSV causes an annual epidemic of respiratory tract illness in infants and in elderly. Mechanisms by which RSV antagonizes IFN-mediated antiviral responses include inhibition of type I IFN mRNA transcription and blocking signal transduction of JAK/STAT family members. The suppressor of cytokines signaling (SOCS) gene family utilizes a feedback loop to inhibit cytokine responses and block the activation of the JAK/STAT signaling pathway. To evaluate the potential of SOCS molecules to subvert the innate immune response to RSV infection, eight SOCS family genes were examined. RSV infection up-regulated SOCS1, SOCS3, and CIS mRNA expression in HEp-2 cells. Suppression of SOCS1, SOCS3 and CIS by short interfering ribonucleic acid (siRNA) inhibited viral replication. Furthermore, inhibition of SOCS1, SOCS3, or CIS activated type I IFN signaling by inducing STAT1/2 phosphorylation. These results suggest that RSV infection escapes the innate antiviral response by inducing SOCS1, SOCS3 or CIS expression in epithelial cells.

Hepatitis delta virus inhibits alpha interferon signaling

Hepatitis delta virus (HDV) can cause severe acute and chronic liver disease in patients infected with hepatitis B virus. Interferon-alpha (IFN-alpha) is the only treatment reported to be effective in chronic hepatitis delta, albeit in a minority of patients. The molecular mechanisms underlying resistance to therapy are unclear. IFN-alpha-induced activation of the Janus kinase-signal transducer and activator of transcription (JAK-STAT) signaling cascade is essential for the induction of an antiviral state. Interference of HDV with the JAK-STAT pathway could be responsible for the IFN-alpha resistance in chronic hepatitis delta patients. We analyzed IFN-alpha-induced signal transduction through the JAK-STAT pathway in human hepatoma cells transfected with the complete HDV genome. The expression of IFN-alpha-stimulated genes was investigated with reverse transcription real-time polymerase chain reaction (PCR). STATs and JAKs activations were examined by immunofluorescence and immunoblot. The IFN-alpha-stimulated genes coding for the antiviral proteins myxovirus resistance A, double-stranded RNA (dsRNA)-activated protein kinase and 2',5'-oligoadenylate synthetase were down-regulated in HDV-transfected hepatoma cells in response to IFN-alpha treatment. HDV severely impaired the phosphorylation of both STAT1 and STAT2, thus preventing their accumulation in the nucleus. Furthermore, HDV blocked the IFN-alpha-stimulated tyrosine phosphorylation of IFN receptor-associated JAK kinase Tyk2, without affecting either the tyrosine phosphorylation of Jak1 or the expression of type I IFN receptor subunits.

CONCLUSIONS

IFN-alpha-induced intracellular signaling is impaired in HDV-transfected human hepatoma cells. HDV subverts the effect of IFN-alpha by blocking Tyk2 activation, thereby resulting in selective impairment of activation and translocation to the nucleus of STAT1 and STAT2. Interference of HDV with IFN-alpha signaling could represent an important mechanism of viral persistence and treatment resistance.

The negative regulatory roles of suppressor of cytokine signaling proteins in myeloid signaling pathways

PURPOSE OF REVIEW

Suppressor of cytokine signaling proteins are key regulators of the response of myeloid cells to cytokines and other extracellular stimuli. This review explores recent developments that have shed light on how two of the best-characterized suppressor of cytokine signaling proteins, SOCS1 and SOCS3, attenuate myeloid signaling pathways that lead to inflammation, hematological malignancy, and related disorders.

RECENT FINDINGS

In addition to its 'classic' role as an inhibitor of IFNgamma signaling, a number of new regulatory roles in IFNalpha and toll-like receptor signaling have been defined for SOCS1, and substantial progress has been made in identifying the factors that give rise to lethal inflammation in Socs1 neonatal mice. The aberrant transcriptional regulation of suppressor of cytokine signaling genes in myeloid leukemia and related proliferative disorders has also been further defined. Finally, positive signs have emerged in mice that exogenous delivery of SOCS3 may be of therapeutic value.

SUMMARY

Suppressor of cytokine signaling proteins have pivotal roles in attenuating cytokine and toll-like receptor signaling in myeloid cells. Understanding how defective suppressor of cytokine signaling activity contributes to inflammatory and malignant disease promises to create significant new therapeutic opportunities.

A genome-wide search for linkage to asthma phenotypes in the genetics of asthma international network families: evidence for a major susceptibility locus on chromosome 2p

Asthma is a complex disease and the intricate interplay between genetic and environmental factors underlies the overall phenotype of the disease. Families with at least two siblings with asthma were collected from Europe, Australia and the US. A genome scan using a set of 364 families with a panel of 396 microsatellite markers was conducted. Nonparametric linkage analyses were conducted for asthma and three asthma-related phenotypes: bronchial hyper-reactivity (BHR), strict definition of asthma and atopic asthma. Nine chromosomal regions with LOD scores greater than 1.5 were identified (chromosomes 1q, 2p, 3q, 4p, 4q, 6q, 12q, 20p and 21). Linkage refinement analysis was performed for three BHR loci by genotyping single nucleotide polymorphisms at an average marker density of 1 cM. The LOD scores increased to 3.07 at chromosome 4p and 4.58 at chromosome 2p, while the chromosome 6p locus did not refine. The LOD score at the chromosome 2p locus is highly significant on a genome-wide basis. The refined locus covers a region with a physical size of 12.2 Mb. Taken together, these results provide evidence for a major asthma susceptibility locus on chromosome 2p.

Suppressors of cytokine signaling (SOCS) 1 and SOCS3 interact with and modulate fibroblast growth factor receptor signaling

Fibroblast growth factor receptor (FGFR) signaling is transduced by the mitogen-activated protein kinase (MAPK) cascade and the signal transducers and activators of transcription (STATs). Suppressors of cytokine signaling (SOCS) proteins are expressed in response to cytokine-inducible stimulation of STAT phosphorylation, acting in a negative-feedback mechanism to hinder the activities of these receptors. However, there are no data concerning the role of SOCS proteins in the regulation of fibroblast growth factor receptor (FGFR) signaling. In the present study, we show that activation of FGFR in chondrocytes induces the expression of SOCS1 and SOCS3 mRNA, and that these proteins are constitutively associated with FGFR3, as demonstrated by co-immunoprecipitation studies. Transfection of cells with FGFR3-GFP and SOCS1-CFP revealed their colocalization, clustered prominently in the perinuclear cytosolic part of the cell. The effect of the interaction between FGFR3 and SOCS1 on receptor activity was investigated in a chondrocytic cell line overexpressing SOCS1. In these cells, STAT1 phosphorylation is repressed, MAPK phosphorylation is elevated and prolonged, and FGFR3 downregulation is attenuated. Expression of osteopontin (OPN), which is directly upregulated by FGF in chondrocytes, was stimulated by lower levels of FGF in cells expressing SOCS1 compared with parental cells. Blocking of MAPK phosphorylation by PD98059 decreased OPN expression in both cell types, but this decrease was more marked in cells expressing SOCS1. The presented results suggest a novel interaction between the SOCS1 and SOCS3 proteins and the FGFR3 signaling pathway.

Murine megakaryocyte progenitor cells and their susceptibility to suppression by G-CSF

In agar cultures of mouse bone marrow cells, mega-karyocyte colony-forming cells exhibited shorter survival times than granulocyte-macrophage progenitor cells when initially cultured in the absence of stimulating factors. Initiation of cultures with G-CSF improved the survival times of granulocyte-macrophage progenitor cells and those of megakaryocyte progenitor cells. Paradoxically, G-CSF was found to consistently inhibit megakaryocyte colony formation stimulated by erythropoietin or by stem cell factor plus interleukin-3 (IL-3) plus erythropoietin. G-CSF was a less-consistent inhibitor of megakaryocyte colonies stimulated by thrombopoietin or IL-3. Analysis of the response of marrow cells from mice with the deletion of the genes encoding CIS, SOCS-1, SOCS-2, SOCS-3, SOCS-5, SOCS-6, or SOCS-7 indicated that the inhibitory SOCS proteins, with the possible exception of SOCS-3, were not involved in the G-CSF-initiated suppression of megakaryocyte colony formation.

SOCS5 mRNA levels in peripheral blood mononuclear cells (PBMC): a potential bio-marker for monitoring response of uveitis patients to Daclizumab therapy

Uveitis is an intraocular inflammatory disease mediated by Th1 lymphocytes. Therapy for severe uveitis is frequently long-term immunosuppression using systemic corticosteroids and cytotoxic agents, but side effects make long-term therapy difficult. Long-term humanized anti-interleukin-2 (IL-2) receptor alpha (Daclizumab) therapy has few side effects and is as effective as standard immunosuppression for treating severe uveitis. However, it is necessary to carefully monitor levels of activated T cells in the eye to allow prompt re-institution of standard immunosuppressive therapy to non-responders to Daclizumab therapy. Suppressors of cytokine signaling (SOCS) are feedback regulators of Th1/Th2 cytokines. SOCS5 and SOCS3 are preferentially expressed in Th1 and Th2 cells, respectively, and are thought to be lineage markers for T-helper cells. In this study, we have investigated whether SOCS3 or SOCS5 expression can serve as surrogate markers of T-cell levels in the eye. Compared to healthy volunteers, SOCS5 mRNA is significantly elevated in PBMC of uveitis patients while SOCS3 is decreased. However, after Daclizumab therapy SOCS5 mRNA level is significantly decreased, suggesting that SOCS5 mRNA can be used as diagnostic tool to monitor therapeutic response of uveitis patients. Our data also suggest that SOCS5 may serve as a new therapeutic target for uveitis and other autoimmune diseases.

Dendritic Cell Maturation Requires STAT1 and Is under Feedback Regulation by Suppressors of Cytokine Signaling

In this study we show that activation of STAT pathways is developmentally regulated and plays a role in dendritic cell (DC) differentiation and maturation. The STAT6 signaling pathway is constitutively activated in immature DC (iDC) and declines as iDCs differentiate into mature DCs (mDCs). However, down-regulation of this pathway during DC differentiation is accompanied by dramatic induction of suppressors of cytokine signaling 1 (SOCS1), SOCS2, SOCS3, and cytokine-induced Src homology 2-containing protein expression, suggesting that inhibition of STAT6 signaling may be required for DC maturation. In contrast, STAT1 signaling is most robust in mDCs and is not inhibited by the up-regulated SOCS proteins, indicating that STAT1 and STAT6 pathways are distinctly regulated in maturing DC. Furthermore, optimal activation of STAT1 during DC maturation requires both IL-4 and GM-CSF, suggesting that synergistic effects of both cytokines may in part provide the requisite STAT1 signaling intensity for DC maturation. Analyses of STAT1(-/-) DCs reveal a role for STAT1 in repressing CD86 expression in precursor DCs and up-regulating CD40, CD11c, and SOCS1 expression in mDCs. We further show that SOCS proteins are differentially induced by IL-4 and GM-CSF in DCs. SOCS1 is primarily induced by IL-4 through a STAT1-dependent mechanism, whereas SOCS3 is induced mainly by GM-CSF. Taken together, these results suggest that cytokine-induced maturation of DCs is under feedback regulation by SOCS proteins and that the switch from constitutive activation of the STAT6 pathway in iDCs to predominant use of STAT1 signals in mDC is mediated in part by STAT1-induced SOCS expression.

Opposing roles of STAT1 and STAT3 in T cell-mediated hepatitis: regulation by SOCS

T cell-mediated fulminant hepatitis is a life-threatening event for which the underlying mechanism is not fully understood. Injection of concanavalin A (Con A) into mice recapitulates the histological and pathological sequelae of T cell-mediated hepatitis. In this model, both signal transducer and activator of transcription factor 1 (STAT1) and STAT3 are activated in the liver. Disruption of the STAT1 gene by way of genetic knockout attenuates liver injury, suppresses CD4(+) and NK T cell activation, and downregulates expression of proapoptotic interferon regulatory factor-1 protein and suppressor of cytokine signaling-1 (SOCS1), but enhances STAT3 activation and STAT3-controlled antiapoptotic signals. Studies from IFN-gamma-deficient mice indicate that IFN-gamma not only is the major cytokine responsible for STAT1 activation but also partially accounts for STAT3 activation. Moreover, downregulation of STAT3 activation in IL-6-deficient mice is associated with decreased STAT3-controlled antiapoptotic signals and expression of SOCS3, but upregulation of STAT1 activation and STAT1-induced proapoptotic signals and exacerbation of liver injury. Taken together, these findings suggest that STAT1 plays a harmful role in Con A-mediated hepatitis by activation of CD4(+) and NK T cells and directly inducing hepatocyte death, whereas STAT3 protects against liver injury by suppression of IFN-gamma signaling and induction of antiapoptotic protein Bcl-X(L). STAT1 and STAT3 in hepatocytes also negatively regulate one another through the induction of SOCS.

Opposing roles of STAT1 and STAT3 in T cell-mediated hepatitis: regulation by SOCS

T cell-mediated fulminant hepatitis is a life-threatening event for which the underlying mechanism is not fully understood. Injection of concanavalin A (Con A) into mice recapitulates the histological and pathological sequelae of T cell-mediated hepatitis. In this model, both signal transducer and activator of transcription factor 1 (STAT1) and STAT3 are activated in the liver. Disruption of the STAT1 gene by way of genetic knockout attenuates liver injury, suppresses CD4(+) and NK T cell activation, and downregulates expression of proapoptotic interferon regulatory factor-1 protein and suppressor of cytokine signaling-1 (SOCS1), but enhances STAT3 activation and STAT3-controlled antiapoptotic signals. Studies from IFN-gamma-deficient mice indicate that IFN-gamma not only is the major cytokine responsible for STAT1 activation but also partially accounts for STAT3 activation. Moreover, downregulation of STAT3 activation in IL-6-deficient mice is associated with decreased STAT3-controlled antiapoptotic signals and expression of SOCS3, but upregulation of STAT1 activation and STAT1-induced proapoptotic signals and exacerbation of liver injury. Taken together, these findings suggest that STAT1 plays a harmful role in Con A-mediated hepatitis by activation of CD4(+) and NK T cells and directly inducing hepatocyte death, whereas STAT3 protects against liver injury by suppression of IFN-gamma signaling and induction of antiapoptotic protein Bcl-X(L). STAT1 and STAT3 in hepatocytes also negatively regulate one another through the induction of SOCS.

MAPPIT: a cytokine receptor-based two-hybrid method in mammalian cells

Identifying novel targets for therapy in allergic disease: protein interactions inside the cell Therapy of allergic disease currently relies on pharmacological manipulation of mediators or immunotherapy. Drugs have been developed to target specific mediators and their receptors: for example antihistamines blocking the H1 receptor have been refined to maximize antagonism and reduce central side-effects or adverse effects of activity on other receptors such as muscarinic cholinergic receptors. Traditional pharmacological approaches identify new surface receptors against which chemists will then design or screen compounds for activity: examples are H3 or H4 histamine receptors. With the advent of the sequenced human genome we are faced with a vast array of genes and proteins that interact to define normal physiology or indeed pathology. A major challenge to biotechnology is to evolve novel techniques to understand the function and interaction of these myriad proteins. One particular area of current interest is the signalling cascades downstream of surface receptors. For many years pathways have appeared overlapping and to offer little chance of specific intervention. However, greater understanding of the complexity and integration of signalling, together with the possibility of directing drugs to specific cells has aroused considerable interest in this area for novel therapeutics. Indeed, targeting events within the cell has been done for many years with steroids. Here, Jan Tavernier and colleagues describe some signalling pathways relevant to allergic disease and potential methods for understanding protein interactions that allow mapping of the cascades. In particular they describe an elegant new system of analysis of protein-protein interactions in a mammalian system, which they have developed, termed MAPPIT. The basis of the system is an engineered receptor with JAK kinase but which lacks STAT activation sites. To the cytoplasmic end of the receptor is added a bait protein of interest, and the cell line can then be transduced with plasmid containing 'prey' cDNA from a library of interest linked to an active STAT binding site. If this cDNA encodes a protein which, upon expression, is activated and recruited to the membrane complex, it will bind to the receptor via the bait, then STAT activation will occur and activate a reporter gene system such as luciferase or puromycin resistance. This novel system allows study of known protein-protein interactions by targeted mutagenesis, or screening for novel interactions. It has the advantage over existing systems such as yeast 2 hybrid that it uses mammalian cells and thus can reproduce the physiological conditions for protein processing or activation. As new genes and proteins are linked to the atopic phenotypes, systems such as this hold promise of rapidly defining their function and interacting proteins and may be important in linking genomics and proteomics with function and pharmacology in the future.

Cooperative effects of Th2 cytokines and allergen on normal and asthmatic bronchial epithelial cells

In sensitized individuals, exposure to allergens such as Dermatophagoides pteronyssinus (Der p) causes Th2 polarization and release of cytokines, including IL-4 and IL-13. Because Der p extracts also have direct effects on epithelial cells, we hypothesized that allergen augments the effects of Th2 cytokines by promoting mediator release from the bronchial epithelium in allergic asthma. To test our hypothesis, primary bronchial epithelial cultures were grown from bronchial brushings of normal and atopic asthmatic subjects. RT-PCR showed that each culture expressed IL-4R(alpha), common gamma-chain, and IL-13R(alpha)(1), as well as IL-13R(alpha)(2), which negatively regulates IL-13 signaling; FACS analysis confirmed IL-13R(alpha)(2) protein expression. Exposure of epithelial cultures to either Der p extracts, TNF-alpha, IL-4, or IL-13 enhanced GM-CSF and IL-8 release, and this was partially suppressible by corticosteroids. Simultaneous exposure of the epithelial cultures to IL-4 or IL-13 together with Der p resulted in a further increase in cytokine release, which was at least additive. Release of TGF-alpha was also increased by TNF-alpha and combinations of IL-4, IL-13, and Der p; however, this stimulation was only significant in the asthma-derived cultures. These data suggest that, in an allergic environment, Th2 cytokines and allergen have the potential to sustain airway inflammation through a cooperative effect on cytokine release by the bronchial epithelium. Our novel finding that IL-4, IL-13, and allergen enhance release of TGF-alpha, a ligand for the epidermal growth factor receptor that stimulates fibroblast proliferation and goblet cell differentiation, provides a potential link between allergen exposure, Th2 cytokines, and airway remodelling in asthma.

Suppressors of cytokine signaling proteins are differentially expressed in Th1 and Th2 cells: implications for Th cell lineage commitment and maintenance

Positive regulatory factors induced by IL-12/STAT4 and IL-4/STAT6 signaling during T cell development contribute to polarized patterns of cytokine expression manifested by differentiated Th cells. These two critical and antagonistic signaling pathways are under negative feedback regulation by a multimember family of intracellular proteins called suppressor of cytokine signaling (SOCS). However, it is not known whether these negative regulatory factors also modulate Th1/Th2 lineage commitment and maintenance. We show here that CD4(+) naive T cells constitutively express low levels of SOCS1, SOCS2, and SOCS3 mRNAs. These mRNAs and their proteins increase significantly in nonpolarized Th cells after activation by TCR signaling. We further show that differentiation into Th1 or Th2 phenotype is accompanied by preferential expression of distinct SOCS mRNA transcripts and proteins. SOCS1 expression is 5-fold higher in Th1 than in Th2 cells, whereas Th2 cells contain 23-fold higher levels of SOCS3. We also demonstrate that IL-12-induced STAT4 activation is inhibited in Th2 cells that express high levels of SOCS3 whereas IL-4/STAT6 signaling is constitutively activated in Th2 cells, but not Th1 cells, with high SOCS1 expression. These results suggest that mutually exclusive use of STAT4 and STAT6 signaling pathways by differentiated Th cells may derive in part, from SOCS3- or SOCS1-mediated repression of IL-12/STAT4- or IL-4/STAT6 signaling in Th2 and Th1 cells, respectively. Given the strong correlation between distinct patterns of SOCS expression and differentiation into the Th1 or Th2 phenotype, SOCS1 and SOCS3 proteins are therefore Th lineage markers that can serve as therapeutic targets for immune modulation therapy.

Signaling through the JAK/STAT pathway, recent advances and future challenges

Investigation into the mechanism of cytokine signaling led to the discovery of the JAK/STAT pathway. Following the binding of cytokines to their cognate receptor, signal transducers and activators of transcription (STATs) are activated by members of the janus activated kinase (JAK) family of tyrosine kinases. Once activated, they dimerize and translocate to the nucleus and modulate the expression of target genes. During the past several years significant progress has been made in the characterization of the JAK/STAT signaling cascade, including the identification of multiple STATs and regulatory proteins. Seven STATs have been identified in mammals. The vital role these STATs play in the biological response to cytokines has been demonstrated through the generation of murine 'knockout' models. These mice will be invaluable in carefully elucidating the role STATs play in regulating the host response to various stresses. Similarly, the solution of the crystal structure of two STATs has and will continue to facilitate our understanding of how STATs function. This review will highlight these exciting developments in JAK/STAT signaling.

Expression of interferon alfa signaling components in human alcoholic liver disease

Interferon alfa (IFN-alpha) is currently the only well-established therapy for viral hepatitis. However, its effectiveness is much reduced (<10%) in alcoholic patients. The mechanism underlying this resistance is not fully understood. In this study, we examined the expression of IFN-alpha signaling components and its inhibitory factors in 9 alcoholic liver disease (ALD) and 8 healthy control liver tissues. In comparison with normal control livers, expression of IFN-beta, IFN-alpha receptor 1/2, Jak1, and Tyk2 remained unchanged in ALD livers, whereas expression of IFN-alpha, signal transducer and activator of transcription factor 1 (STAT1), and p48 were up-regulated and expression of STAT2 was down-regulated. Expression of antiviral MxA a karyophilic 75 kd protein induced by IFN in mouse cells carrying the influenza virus resistance allele Mx(+) and 2'-5' oligoadenylate synthetase (OAS) proteins was not regulated, whereas expression of double-stranded RNA-activated protein kinase (PKR) was decreased by 55% in ALD livers. Three families of inhibitory factors for the JAK-STAT signaling pathway were examined in ALD livers. Members of the suppressor of cytokine signaling (SOCS) family, including SOCS 1, 2, 3, and CIS, and the protein tyrosine phosphatases, including Shp-1, Shp-2, and CD45, were not up-regulated in ALD livers, whereas the phosphorylation of and protein levels of p42/44 mitogen-activated protein kinase (p42/44MAP kinase) were increased about 3.9- and 3.2-fold in ALD livers in comparison with normal control livers, respectively. In conclusion, these findings suggest that chronic alcohol consumption down-regulates STAT2 and PKR, but up-regulates p42/44 mitogen-activated protein kinase (p42/44MAP kinase), which may cause down-regulation of IFN-alpha signaling in the liver of ALD patients.

Production of colony-stimulating factors and IL-5 by organs from three types of mice with inflammatory disease due to loss of the suppressor of cytokine signaling-1

Organs from neonatal mice dying from IFN-gamma-dependent inflammatory disease initiated by loss of the gene encoding the suppressor of cytokine signaling-1 (SOCS-1) had a normal capacity to produce G-CSF in vitro but a reduced capacity to produce GM-CSF, most evident with the lung, and some reduction in the production of M-CSF by muscle tissue. In contrast, organs from mice lacking the genes for both SOCS-1 and IFN-gamma had a normal capacity to produce CSFs. Organs from young adult mice dying with polymyositis and myocarditis that lacked SOCS-1 but were heterozygous for IFN-gamma had a normal capacity to produce GM-CSF and M-CSF, but muscle tissue produced significantly increased amounts of G-CSF and IL-5 with IL-5 production also being elevated for the salivary gland, thymus, and heart. Loss of the IFN-gamma gene alone had no impact on organ production of these cytokines in vitro. In none of the inflammatory disease models was IL-3 production detected. The SOCS-1 protein appears to have no direct influence on the cellular production of these cytokines and the abnormalities observed either depend on the coaction of IFN-gamma, or more likely, are linked with the invasion and destruction of tissue by T lymphocytes, macrophages, eosinophils, and neutrophils. The ability of local organs to produce these proinflammatory cytokines could contribute to the development and progression of these inflammatory lesions.

Feedback control of intercellular signalling in development

The intercellular communication that regulates cell fate during animal development must be precisely controlled to avoid dangerous errors. How is this achieved? Recent work has highlighted the importance of positive and negative feedback loops in the dynamic regulation of developmental signalling. These feedback interactions can impart precision, robustness and versatility to intercellular signals. Feedback failure can cause disease.

Cytokines and JAK-STAT signaling

Characterization of the ability of IFNs to induce immediate early genes led to the identification of the STAT (signal transducers and activators of transcription) signaling paradigm. STATs are activated at the receptor and then directly transduce signals to the nucleus. Subsequent studies have determined that all cytokines transduce critical signals through this pathway.