A non-classical ISRE/ISGF3 pathway mediates induction of RANTES gene transcription by type I IFNs

Influence of the inflammatory response on treatment of hepatitis C with triple therapy

INTRODUCTION

Chronic hepatitis C is a leading cause of liver disease. Infection triggers an immediate immune response in the host that is mediated by humoral/cellular mechanisms. T cells respond to infection via secretion of cytokines, which inhibit or stimulate one another, leading to cytokine imbalance and ultimately affecting treatment. Studies using interferon (IFN) and ribavirin (RBV) showed that TCD8+ cells and cytokine levels are associated with sustainable virological response (SVR). However, studies that investigated the effects of triple therapy (TT) are limited.

METHODS

The study included hepatitis C virus (HCV)+ RNA, naives, genotype 1, ≥18 years, and advanced fibrosis (F≥3) patients. Samples were collected at baseline and after 12 weeks (W12) of TT. Six cytokines were analyzed by flow cytometry.

RESULTS

Of 31 patients, four were excluded (two deaths, one interrupted TT, and one F2 patient). Of the 27 remaining patients, 21 (78%) were cirrhotic. SVR was achieved in 63% of the patients. The patients had a mean age of 55.11 ± 10.03 years. Analyses at baseline showed that the chemokine CCL5/Regulated on Activation, Normal T Cell Expressed and Secreted (RANTES) (p=0.04) and interleukin (IL)-6 (p=0.02), which was associated with SVR. RANTES (p=0.04) and IL-8 (p=0.01) levels were associated with SVR at W12.

CONCLUSIONS

Similar to patterns observed during double therapy, IL-6, IL-8, and RANTES levels were associated with SVR in TT, indicating the potential role of interferon in immune response to hepatitis C virus.

CCL5: a double-edged sword in host defense against the hepatitis C virus

C-C motif ligand 5 (CCL5) facilitates induction of chemotaxis in immune cells and activation of hepatic stellate cells (HSC) at sites of liver inflammation during chronic hepatitis C virus (HCV) infection. Importantly, CCL5 participates in the establishment of T-helper 1 responses crucial in controlling liver disease and HCV infection outcome and demonstrates distinct gene expression patterns between the blood and the liver, stressing the importance of immunoregulatory networks differentially functioning between these compartments. This review illustrates the significance of CCL5-dependent pathways in HCV-related immunopathogenesis by elaborating on biological mechanisms interconnecting peripheral and tissue immunology, liver pathology, HSC activation, and interferon-α immunotherapy.

Intrinsic adjuvanting of a novel single-cycle flavivirus vaccine in the absence of type I interferon receptor signaling

Type I interferons (IFNs) are critical for controlling pathogenic virus infections and can enhance immune responses. Hence their impact on the effectiveness of live-attenuated vaccines involves a balance between limiting viral antigen expression and enhancing the development of adaptive immune responses. We examined the influence of type I IFNs on these parameters following immunization with RepliVAX WN, a single-cycle flavivirus vaccine (SCFV) against West Nile virus (WNV) disease. RepliVAX WN-immunized mice produced IFN-α and displayed increased IFN-stimulated gene transcription in draining lymph nodes (LN). SCFV gene expression was over 100 fold-higher on days 1-3 post-infection in type I IFN receptor knockout mice (IFNAR(-/-)) compared to wild-type (wt) mice indicating a profound IFN-mediated suppression of SCFV gene expression in the wt animals. IFNAR(-/-) mice produced nearly equivalent levels of WNV-specific serum IgG and WNV-specific CD4(+) T cell responses compared to wt mice. However, significantly higher numbers of WNV-specific CD8(+) T cells were produced by IFNAR(-/-) mice and a significantly greater percentage of these T cells from IFNAR(-/-) mice produced only IFN-γ following antigen-specific re-stimulation. This altered cytokine expression was not associated with increased antigen load suggesting the loss of type I IFN receptor signaling was responsible for the altered quality of the CD8(+) effector T cell response. Together, these results indicate that although type I IFN is not essential for the intrinsic adjuvanting of RepliVAX WN, it plays a role in shaping the cytokine secretion profiles of CD8(+) effector T cells elicited by this SCFV.

Myeloid type I interferon signaling promotes atherosclerosis by stimulating macrophage recruitment to lesions

Inflammatory cytokines are well-recognized mediators of atherosclerosis. Depending on the pathological context, type I interferons (IFNs; IFNalpha and IFNbeta) exert either pro- or anti-inflammatory immune functions, but their exact role in atherogenesis has not been clarified. Here, we demonstrate that IFNbeta enhances macrophage-endothelial cell adhesion and promotes leukocyte attraction to atherosclerosis-prone sites in mice in a chemokine-dependent manner. Moreover, IFNbeta treatment accelerates lesion formation in two different mouse models of atherosclerosis and increases macrophage accumulation in the plaques. Concomitantly, absence of endogenous type I IFN signaling in myeloid cells inhibits lesion development, protects against lesional accumulation of macrophages, and prevents necrotic core formation. Finally, we show that type I IFN signaling is upregulated in ruptured human atherosclerotic plaques. Hereby, we identify type I IFNs as proatherosclerotic cytokines that may serve as additional targets for prevention or treatment.

Association of elevated transcript levels of interferon-inducible chemokines with disease activity and organ damage in systemic lupus erythematosus patients

Introduction

Systemic lupus erythematosus (SLE) is a multi-system autoimmune disease with a heterogeneous course and varying degrees of severity and organ damage; thus, there is increasing interest in identifying biomarkers for SLE. In this study we correlated the combined expression level of multiple interferon-inducible chemokines with disease activity, degree of organ damage and clinical features in SLE, and we investigated their roles as biomarkers.

Methods

Peripheral blood cells obtained from 67 patients with SLE patients, 20 patients with rheumatoid arthritis (RA) and 23 healthy donors were subjected to real-time PCR in order to measure the transcriptional levels of seven interferon-inducible chemokines (RANTES, MCP-1, CCL19, MIG, IP-10, CXCL11, and IL-8). The data were used to calculate a chemokine score for each participant, after which comparisons were performed between various groups of SLE patients and control individuals.

Results

Chemokine scores were significantly elevated in SLE patients versus RA patients and healthy donors (P = 0.012 and P = 0.002, respectively). Chemokine scores were correlated positively with SLE Disease Activity Index 2000 scores (P = 0.005) and negatively with C3 levels (P < 0.001). Compared with patients without lupus nephritis and those with inactive lupus nephritis, chemokine scores were elevated in patients with active lupus nephritis, especially when their daily prednisone dosage was under 30 mg (P = 0.002 and P = 0.014, respectively). Elevated chemokine scores were also associated with the presence of cumulative organ damage (Systemic Lupus International Collaborating Clinics/American Society of Rheumatology Damage Index ≥ 1; P = 0.010) and the occurrence of anti-Sm or anti-RNP autoantibodies (both P = 0.021).

Conclusions

The combined transcription level of interferon-inducible chemokines in peripheral blood leucocytes is closely associated with disease activity, degree of organ damage, and specific autoantibody patterns in SLE. The chemokine score may serve as a new biomarker for active and severe disease in SLE.

IFN-α2 Induces Leukocyte Integrin Redistribution, Increased Adhesion, and Migration

The human type I Interferon (IFN) family includes 14 closely related cytokines that are produced in response to viral and bacterial infections and mediate the progress of innate immune responses to adaptive immune protection, bind to a common receptor, and have qualitatively similar biologic activities. We have shown previously that IFN-alpha2 can induce human T cell chemotaxis, suggesting that type I IFNs may contribute to the development of an inflammatory environment. We here report that, in addition to promoting T cell chemotaxis, IFN-alpha2 enhances T cell adhesion to integrin ligands, which is associated with integrin clustering on the T cell surface and enhanced conjugate formation with dendritic cells. These effects were prevented by inhibition of mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K). As type I IFN receptor is ubiquitously expressed, this analysis was extended to other human leukocyte populations, including granulocytes and B cells. All leukocyte populations analyzed displayed increased chemotaxis, integrin clustering, and increased integrin-mediated adhesion following exposure to IFN-alpha2, revealing a broad-spectrum proinflammatory activity. These findings have obvious implications for the role of type I IFNs in the development of inflammatory responses leading to the initiation of adaptive immunity.

Interferon-β Is a Potent Inducer of Interferon Regulatory Factor-1/2-Dependent IP-10/CXCL10 Expression in Primary Human Endothelial Cells

Most virus-infected cells release interferon-beta (IFN-beta) as a powerful inducer of antiviral defense. Endothelial cells tightly regulate local immune cell recruitment by expression of adhesion molecules and chemokines. Here, we studied the transcriptional regulation of IFN-beta-induced chemokine expression in primary human endothelial cells. IFN-beta moderately increased monocyte chemoattractant protein-1/CCL2 and potently raised IFN-gamma-inducible protein-10/CXCL10 mRNA steady-state levels and protein release, while no effect was detected on various other chemokines. As shown by transient transfections, induction of CXCL10 expression depends on an IFN-stimulated response element (ISRE) within the CXCL10 promoter. A double point mutation of the putative IFN regulatory factor (IRF)-1/2 binding site within this ISRE motif abolished IFN-beta-induced promoter activity. In electrophoretic mobility shift assays, this ISRE motif showed a basal IRF-2 and an IFN-beta-inducible IRF-1 and augmented IRF-2 binding. Furthermore, stimulation with IFN-beta induced a rapid nuclear translocation of signal transducer and activator of transcription 1 (STAT1) and STAT2 and their transient binding to a gamma-activated site within the CCL2 promoter. The kinetics of transient STAT1 binding to this gamma-activated site element correlated with the amount of Y701-phosphorylated nuclear STAT1, while S727-phosphorylated nuclear STAT1 remained stable over 24 h after stimulation. Therefore, IFN-beta potently induces endothelial chemokine expression at the transcriptional level.

Inhibition of vesicular stomatitis virus infection in epithelial cells by alpha interferon-induced soluble secreted proteins

Interferons (IFNs) are potent antiviral cytokines that inhibit infection by a wide spectrum of viruses by activating the Janus kinase/signal transducers and activators of transcription (JAK/STAT) pathway. Several IFN-induced antiviral proteins including 2',5'-oligoadenylate synthetase, dsRNA-activated protein kinase and Mx play a critical role in conferring the antiviral properties of IFN. However, studies have shown that additional antiviral factors are involved in addition to these proteins during IFN-mediated antiviral action. In an effort to characterize these novel antiviral factors, the antiviral mechanism of alpha IFN (IFN-alpha) against vesicular stomatitis virus (VSV) was investigated in human lung epithelial A549 cells. These studies demonstrated that soluble secreted antiviral proteins as the constituents of conditioned medium prepared from IFN-alpha-treated cells reduced VSV infectivity by more than 2 logs, compared with a 4 log inhibition observed following treatment of cells with IFN-alpha. The antiviral mechanism of these secreted proteins appeared to act at the level of cellular entry of VSV. Interestingly, the IFN-alpha-induced antiviral proteins were secreted independently of STAT1 (an essential component of the JAK/STAT pathway), demonstrating that the release of such extracellular soluble antiviral proteins from cells may represent an alternative mechanism of the antiviral defence strategy of IFN towards VSV infection.

Nonclassical pathway of Pseudomonas aeruginosa DNA-induced interleukin-8 secretion in cystic fibrosis airway epithelial cells

Pseudomonas aeruginosa is a critical colonizer of the respiratory tract in cystic fibrosis. The chronic infections with this microorganism contribute to excessive inflammation and progressive lung damage in cystic fibrosis patients. The full repertoire of Pseudomonas products that promote inflammation in the cystic fibrosis lung is not known. Here we show that P. aeruginosa DNA released from the bacterium, but not human DNA from epithelial cells or Escherichia coli DNA, displays proinflammatory properties and induces human respiratory epithelial cells to secrete interleukin-8 (IL-8), a key chemokine causing excessive neutrophil infiltration in the cystic fibrosis lung. IL-8 secretion was not due to an increase in NF-kappaB- or activator protein-1-dependent IL-8 promoter transcription, but instead depended on p38 and Erk mitogen-activated protein kinases. No secretion of IL-8 was observed using conventional Toll-like receptor 9 ligands (CpG oligonucleotides), although it could be demonstrated that parts of the Toll-like receptor 9-signaling pathway were functional, since class B and C CpG oligonucleotide ligands stimulated production of RANTES chemokine. The IL-8 secretion in response to P. aeruginosa DNA was decreased by treatments that inhibit acidification of intracellular organelles, using chloroquine, a pH-neutralizing compound, or bafilomycin A1, an inhibitor of vacuolar H+-ATPase. These data indicate that DNA released from P. aeruginosa during chronic infections may significantly contribute to the proinflammatory processes in cystic fibrosis. Our findings also show that treatments with drugs diminishing organellar acidification may reduce the inflammatory response in cystic fibrosis.

CCAAT/enhancer binding proteins and interferon signaling pathways

Interferons (IFNs) regulate a number of host responses, including innate and adaptive immunity against viruses, microbes, and neoplastic cells. These responses are dependent on the expression of IFN-stimulated genes (ISGs). Given the diversities in these responses and their kinetics, it is conceivable that a number of different factors are required for controlling them. Here, we describe one such pathway wherein transcription factor CAAAT/enhancer binding protein-beta (C/EBP-beta) is controlled via IFN-gamma-induced MAPK signaling pathways. At least two IFN-gamma-induced MAPK signals converge on to C/EBP-beta for inducing transcription. One of these, driven by extracellular signal-regulated kinases (ERKs), phosphorylates the C/EBP-beta protein in its regulatory domain. The second, driven by the mixed-lineage kinases (MLKs), induces a dephosphorylation leading to the recruitment of transcriptional coactivators.

Subcutaneous interferon-beta injections in patients with multiple sclerosis initiate inflammatory skin reactions by local chemokine induction

Subcutaneous Interferon-beta (IFN-beta) injections for the treatment of multiple sclerosis (MS) frequently cause inflammatory injection site reactions. To study the role of chemokines we obtained skin biopsies from 7 MS patients 24 h after injection. At the IFN-beta but not at the contralateral placebo injection sites, we observed strong IP-10/CXCL10 and moderate MCP-1/CCL2 expression associated with extensive perivascular, highly CXCR3-positive T cell and macrophage infiltrates. Primary human skin cells displayed a comparable pattern of chemokine induction after stimulation with IFN-beta in vitro. IFN-beta may therefore trigger inflammatory skin reactions through local chemokine induction followed by rapid immune cell extravasation.

Involvement of histamine H1 and H2 receptors in the regulation of STAT-1 phosphorylation: inverse agonism exhibited by the receptor antagonists

Signal transducer and activator of transcription-1 (STAT1) is a latent signal transducer protein which, on phosphorylation, is translocated from the cytoplasm to the nucleus and is subsequently activated. This study was designed to determine the involvement of histamine receptors in histamine-mediated effect on STAT1 phosphorylation. It is known that the actions of histamine mediated through H1 and H2 receptors are dependent on their respective downstream pathways, Ca(2+)-PKC and cAMP-PKA. In this study, we investigated the significance of PKA in STAT1 phosphorylation. C57BL/6 mouse splenocytes were isolated and treated with histamine (10(-7)-10(-4) M) and then activated with PMA (phorbol 12 myristate 13-acetate) plus ionomycin. The phosphorylated STAT1 levels were analyzed by immunoblotting. Histamine receptor agonists amthamine and betahistine, histamine receptor antagonists pyrilamine maleate, tripelennamine, ranitidine, cimetidine and thioperamide, cAMP agonists N(6), 2'-0-dibutyryladenosine-3',5'-cyclic monophosphate sodium salt (db-cAMP) and forskolin, protein kinase A inhibitors N-(2-[p-bromocinnamylamino]ethyl)-5-isoquinoline-sulfonamide (H89) and Rp diastereomer of adenosine cyclic 3',5'-phosphorothioate (RpcAMPs) and tyrosine kinase inhibitor tyrphostin were used to identify the upstream signal transduction pathways. We observed that histamine augmented the phosphorylation of STAT1 through both H1 and H2 receptors. Furthermore, H1 and H2 receptor antagonists displayed inverse agonism. Ca(2+)-PKC-induced phosphorylation of STAT1 was completely inhibited by H89 and significantly inhibited by RpcAMPs. DbcAMP and forskolin augmented the Ca(2+)-PKC-induced STAT1 phosphorylation thus suggesting a convergent crosstalk between the two histamine receptor signaling pathways, PKA and PKC.

Interferon-beta induces transient systemic IP-10/CXCL10 chemokine release in patients with multiple sclerosis

Reduction of chemokine expression induced by human recombinant Interferon (IFN)-beta is thought to be a therapeutic mechanism of its action in the treatment of multiple sclerosis (MS). In vitro, IFN-beta can induce chemokine expression. Here we show that a single injection of IFN-beta induced a transient strong increase of IP-10/CXCL10 and a weak elevation of MCP-1/CCL2 plasma levels in MS patients on continuing treatment with IFN-beta. IP-10/CXCL10 bursts, which were not observed in glatiramer acetate (GA)-treated patients, correlated with occurrence of flu-like symptoms. Systemic IP-10/CXCL10 release induced by IFN-beta may influence its therapeutic effect--either negatively or positively.

IFN-α Subtypes Differentially Affect Human T Cell Motility

The type I IFN family includes 14 closely related antiviral cytokines that are produced in response to viral infections. They bind to a common receptor, and have qualitatively similar biological activities. The physiological relevance of this redundancy is still unclear. In this study, we analyzed and compared the effects of two potent antiviral type I IFNs, IFN-alpha 2 and IFN-alpha 8, on the motility of various populations of human T lymphocytes in vitro. In this study, we show that IFN-alpha 2 induces chemokinesis of both CD4(+) and CD8(+) T cells at various stages of differentiation, and induces functional changes that result in enhanced T cell motility, including up-regulation of the integrins LFA-1 and VLA-4, and subsequently, increased ICAM-1- and fibronectin-dependent migration. In contrast, IFN-alpha 8 did not affect T cell motility, despite having similar antiviral properties and similar effects on the induction of the antiviral protein MxA. However, transcription of other IFN-stimulated genes showed that transcription of these genes is selectively activated by IFN-alpha 2, but not IFN-alpha 8, in T cells. Finally, while the antiviral activity of the two subtypes is inhibited by Abs against the two subunits of the IFN-alpha receptor, the chemokinetic effect of IFN-alpha 2 is selectively blocked by Abs against the A1 receptor subunit. These observations are consistent with the possibility that subtype-specific intracellular signaling pathways are activated by type I IFNs in T lymphocytes.

Oxidized Low Density Lipoprotein Blocks Lipopolysaccharide-induced Interferon β Synthesis in Human Macrophages by Interfering with IRF3 Activation

In response to lipopolysaccharide (LPS) exposure, macrophages activate the transcription of a large number of pro-inflammatory genes by way of signaling pathways downstream of the LPS receptor, Toll-Like Receptor 4. Many of these genes are expressed sequentially in time, with early synthesis events resulting in the secretion of soluble factors that drive the transcription of genes expressed later in the activation cycle. In this study we show that human blood-derived macrophages pretreated with oxidized low density lipoprotein (OxLDL) fail to transcribe and secrete interferon beta (IFNbeta) immediately following LPS stimulation. As such, the normal downstream activation of Stat1 is blocked, and numerous IFNbeta/Stat1-activated genes, including the chemokines IP10 and ITAC, are weakly expressed or not expressed at all in these cells. Inspection of the LPS-induced activation state of several transcription factors known to play a prominent role in IFNbeta transcription reveals that, although NFkappaB, c-Jun, and ATF-2 activation appears normal, the LPS-induced activation of IFNbeta regulatory factor 3 (IRF3), as measured by DNA-binding activity and association with the coactivator CBP, is inhibited in the OxLDL pre-treated cells. These IRF3 activities have been shown to be essential for the initiation of transcription of the IFNbeta gene, and the loss of these activities presumably accounts for the lack of LPS-induced IFN beta transcription seen in the OxLDL pre-treated cells.

Alternate interferon signaling pathways

More than a half a century ago, interferons (IFN) were identified as antiviral cytokines. Since that discovery, IFN have been in the forefront of basic and clinical cytokine research. The pleiotropic nature of these cytokines continues to engage a large number of investigators to define their actions further. IFN paved the way for discovery of Janus tyrosine kinase (JAK)-signal transducing activators of transcription (STAT) pathways. A number of important tumor suppressive pathways are controlled by IFN. Several infectious pathogens counteract IFN-induced signaling pathways. Recent studies indicate that IFN activate several new protein kinases, including the MAP kinase family, and downstream transcription factors. This review not only details the established IFN signaling paradigms but also provides insights into emerging alternate signaling pathways and mechanisms of pathogen-induced signaling interference.

Signaling pathways regulating interleukin-13-stimulated chemokine release from airway smooth muscle

Interleukin (IL)-13 receptor activation on airway smooth muscle cells induces eotaxin release and activates multiple signaling pathways including mitogen-activated protein kinases, and signal transducer and activator of transcription 6 (STAT6). To examine a requirement for STAT6 in mediating IL-13-stimulated eotaxin release we used antisense oligodeoxynucleotides (ODNs) to downregulate endogenous STAT6 protein. STAT6 antisense ODNs were taken up by about 85% of cells. Selective downregulation of STAT6 protein occurred with antisense ODNs, but not with sense or scrambled ODNs. Eotaxin release induced by IL-13 or IL-4 (10 ng/ml) was reduced by 81 +/- 4 and 75 +/- 7%, respectively, in cells transfected with antisense ODNs (p < 0.001), but not with a sense ODN or a scrambled ODN. Eotaxin release induced by IL-1beta was unaffected by STAT6 antisense ODN (p > 0.05). Finally, IL-13- or IL-4-dependent eotaxin release was abolished when inhibitors of both p42/p44 ERK (U0126, 10 microM) and p38 (SB202190, 10 microM) mitogen-activated protein kinase pathways were combined in STAT6 antisense ODN-transfected cells. In contrast, about 25% of the response remained when each inhibitor was examined alone in STAT6 antisense ODN-treated cells. These data support roles for both STAT6- and mitogen-activated protein kinase-dependent pathways in mediating eotaxin release from airway smooth muscle by IL-13 or IL-4.

Tumor necrosis factor alpha modulates airway smooth muscle function via the autocrine action of interferon beta

Current evidence suggests that tumor necrosis factor alpha (TNFalpha) and the family of interferons (IFNs) synergistically regulate many cellular responses that are believed to be critical in chronic inflammatory diseases, although the underlying mechanisms of such interaction are complex, cell-specific, and not completely understood. In this study, TNFalpha in a time-dependent manner activated both janus tyrosine kinase 1 and Tyk2 tyrosine kinase and increased the nuclear translocation of interferon-regulatory factor-1, STAT1, and STAT2 in human airway smooth muscle cells. In cells transfected with a luciferase reporter, TNFalpha stimulated gamma-activated site-dependent gene transcription in a time- and concentration-dependent manner. Using neutralizing antibodies to IFNbeta and TNFalpha receptor 1, we show that TNFalpha-induced secretion of IFNbeta mediated gamma-activated site-dependent gene expression via activation of TNFalpha receptor 1. In addition, neutralizing antibody to IFNbeta also completely abrogated the activation of interferon stimulation response element-dependent gene transcription induced by TNFalpha. Secreted IFNbeta acted as a negative regulator of TNFalpha-induced interleukin-6 expression, while IFNbeta augmented TNFalpha-induced RANTES (regulated on activation normal T cell expressed and secreted) secretion but had little effect on TNFalpha-induced intercellular adhesion molecule-1 expression. Furthermore TNFalpha, a modest airway smooth muscle mitogen, markedly induced DNA synthesis when cells were treated with neutralizing anti-IFNbeta. Together these data show that TNFalpha, via the autocrine action of IFNbeta, differentially regulates the expression of proinflammatory genes and DNA synthesis.

Respiratory syncytial virus infection activates STAT signaling in human epithelial cells

Acute respiratory syncytial virus (RSV) infection causes airway inflammation and exacerbates asthma, but the mechanism of inflammation is poorly understood. The role of the STAT-signaling pathway in RSV infection in epithelial cells was examined in this study. DNA microarray analyses of RSV-infected human alveolar type II (A549) epithelial cells identified several genes whose expression was altered from -5.5 to +56.4-fold. Four of the highly expressed genes contained STAT-binding elements. In A549 and normal human bronchial epithelial cells (NHBE), RSV induced phosphorylation and nuclear translocation of STAT-1alpha that was abrogated when RSV attachment was blocked. Treatment with a JAK-2 inhibitor or transfection with dominant-negative STAT-1alpha blocked STAT-1alpha activation and RSV infection. RSV also activated STAT-3 and IL-6 specific antibodies blocked this activation. Thus, activation of the STAT-1alpha and STAT-3 pathways play a role in RSV infection.

A novel transactivating factor that regulates interferon-gamma-dependent gene expression

We have previously identified a novel interferon (IFN)-stimulated cis-acting enhancer element, gamma-IFN-activated transcriptional element (GATE). GATE differs from the known IFN-stimulated elements in its primary sequence. Preliminary analysis has indicated that the GATE-dependent transcriptional response requires the binding of novel transacting factors. A cDNA expression library derived from an IFN-gamma-stimulated murine macrophage cell line was screened with a (32)P-labeled GATE probe to identify the potential GATE-binding factors. A cDNA coding for a novel transcription-activating factor was identified. Based on its discovery, we named it as GATE-binding factor-1 (GBF-1). GBF-1 homologs are present in mouse, human, monkey, and Drosophila. It activates transcription from reporter genes carrying GATE. It possesses a strong transactivating activity but has a weak DNA binding property. GBF-1 is expressed in most tissues with relatively higher steady-state levels in heart, liver, kidney, and brain. Its expression is induced by IFN-gamma treatment. GBF-1 is present in both cytosolic and nuclear compartments. These studies thus identify a novel transactivating factor in IFN signaling pathways.

Review: IFN-alpha/beta receptor interactions to biologic outcomes: understanding the circuitry

Type I interferons (IFNs), which include the IFN-alphas, IFN-beta, IFN-omega, IFN-kappa, and IFN-tau, are an evolutionarily conserved group of secreted cytokines that serve as potent extracellular mediators of host defense and homeostasis. Binding of IFNs to specific cell surface receptors results in the activation of multiple intracellular signaling cascades, leadingto the synthesis of proteins that mediate antiviral, growth inhibitory and immunomodulatory responses. In the past decade, considerable information has accumulated pertaining to the different signalingpathways that are activated by the type I IFNs. Although many of the literature findings are specific to defined cell systems or are tissue restricted, the intent of this review is to place these signaling cascades and their effectors in the context of distinct biologic outcomes.