The human type I interferon receptor. Identification of the interferon beta-specific receptor-associated phosphoprotein

The primitive interferon-like system and its antiviral function in molluscs

The phylum mollusca is a very important group in the animal kingdom for the large number and diversified species. Recently, interest in molluscan immunity has increased due to their phylogenetic position and importance in worldwide aquaculture and aquatic environment. As the main aquaculture animal, most molluscs live in the water environment and they have to cope with many pathogen challenges, in which virus is one of the primary causes for the mass mortality. In vertebrates, interferon (IFN) system is generally recognized as the first line of defence against viral infection, while the antiviral mechanisms in molluscs remain to be clearly illuminated. Recently, some IFN-like proteins and IFN-related components have been characterized from molluscs, such as pattern recognition receptors (PRRs), interferon regulatory factors (IRFs), IFN-like receptors, JAK/STAT and IFN-stimulated genes (ISGs), which reinforce the existence of IFN-like system in molluscs. This system can be activated by virus or poly (I:C) challenges and further regulate the antiviral response of haemocytes in molluscs. This review summarizes the research progresses of IFN-like system in molluscs with the emphases on the uniformity and heterogeneity of IFN-like system of molluscs compared to that of other animals, which will be helpful for elucidating the antiviral modulation in molluscs and understanding the origin and evolution of IFN system.

Opposing Roles of Type I Interferons in Cancer Immunity

The immune system is tasked with identifying malignant cells to eliminate or prevent cancer spread. This involves a complex orchestration of many immune cell types that together recognize different aspects of tumor transformation and growth. In response, tumors have developed mechanisms to circumvent immune attack. Type I interferons (IFN-Is) are a class of proinflammatory cytokines produced in response to viruses and other environmental stressors. IFN-Is are also emerging as essential drivers of antitumor immunity, potently stimulating the ability of immune cells to eliminate tumor cells. However, a more complicated role for IFN-Is has arisen, as prolonged stimulation can promote feedback inhibitory mechanisms that contribute to immune exhaustion and other deleterious effects that directly or indirectly permit cancer cells to escape immune clearance. We review the fundamental and opposing functions of IFN-Is that modulate tumor growth and impact immune function and ultimately how these functions can be harnessed for the design of new cancer therapies.

Activation of the JAK-STAT Signaling Pathway after In Vitro Stimulation with IFNß in Multiple Sclerosis Patients According to the Therapeutic Response to IFNß

Interferon beta (IFNß) is a common treatment used for multiple sclerosis (MS) which acts through the activation of the JAK-STAT pathway. However, this therapy is not always effective and currently there are no reliable biomarkers to predict therapeutic response. We postulate that the heterogeneity in the response to IFNß therapy could be related to differential activation patterns of the JAK-STAT signaling pathway. Our aim was to evaluate the basal levels and the short term activation of this pathway after IFNß stimulation in untreated and IFNß treated patients, as well as according to therapeutic response. Therefore, cell surface levels of IFNAR subunits (IFNAR1 and IFNAR2) and the activated forms of STAT1 and STAT2 were assessed in peripheral blood mononuclear cells from MS patients by flow cytometry. Basal levels of each of the markers strongly correlated with the expression of the others in untreated patients, but many of these correlations lost significance in treated patients and after short term activation with IFNß. Patients who had undergone IFNß treatment showed higher basal levels of IFNAR1 and pSTAT1, but a reduced response to in vitro exposure to IFNß. Conversely, untreated patients, with lower basal levels, showed a greater ability of short term activation of this pathway. Monocytes from responder patients had lower IFNAR1 levels (p = 0.039) and higher IFNAR2 levels (p = 0.035) than non-responders just after IFNß stimulation. A cluster analysis showed that levels of IFNAR1, IFNAR2 and pSTAT1-2 in monocytes grouped 13 out of 19 responder patients with a similar expression pattern, showing an association of this pattern with the phenotype of good response to IFNß (p = 0.013). Our findings suggest that an activation pattern of the IFNß signaling pathway in monocytes could be associated with a clinical phenotype of good response to IFNß treatment and that a differential modulation of the IFNAR subunits in monocytes could be related with treatment effectiveness.

Type I Interferons Function as Autocrine and Paracrine Factors to Induce Autotaxin in Response to TLR Activation

Lysophosphatidic acid (LPA) is an important phospholipid mediator in inflammation and immunity. However, the mechanism of LPA regulation during inflammatory response is largely unknown. Autotaxin (ATX) is the key enzyme to produce extracellular LPA from lysophosphatidylcholine (LPC). In this study, we found that ATX was induced in monocytic THP-1 cells by TLR4 ligand lipopolysaccharide (LPS), TLR9 ligand CpG oligonucleotide, and TLR3 ligand poly(I:C), respectively. The ATX induction by TLR ligand was abolished by the neutralizing antibody against IFN-β or the knockdown of IFNAR1, indicating that type I IFN autocrine loop is responsible for the ATX induction upon TLR activation. Both IFN-β and IFN-α were able to induce ATX expression via the JAK-STAT and PI3K-AKT pathways but with different time-dependent manners. The ATX induction by IFN-β was dramatically enhanced by IFN-γ, which had no significant effect on ATX expression alone, suggesting a synergy effect between type I and type II IFNs in ATX induction. Extracellular LPA levels were significantly increased when THP-1 cells were treated with IFN-α/β or TLR ligands. In addition, the type I IFN-mediated ATX induction was identified in human monocyte-derived dendritic cells (moDCs) stimulated with LPS or poly(I:C), and IFN-α/β could induce ATX expression in human peripheral blood mononuclear cells (PBMCs) and monocytes isolated form blood samples. These results suggest that, in response to TLR activation, ATX is induced through a type I INF autocrine-paracrine loop to enhance LPA generation.

Multifarious determinants of cytokine receptor signaling specificity

Cytokines play crucial roles in regulating immune homeostasis. Two important characteristics of most cytokines are pleiotropy, defined as the ability of one cytokine to exhibit diverse functionalities, and redundancy, defined as the ability of multiple cytokines to exert overlapping activities. Identifying the determinants for unique cellular responses to cytokines in the face of shared receptor usage, pleiotropy, and redundancy will be essential in order to harness the potential of cytokines as therapeutics. Here, we discuss the biophysical (ligand-receptor geometry and affinity) and cellular (receptor trafficking and intracellular abundance of signaling molecules) parameters that contribute to the specificity of cytokine bioactivities. Whereas the role of extracellular ternary complex geometry in cytokine-induced signaling is still not completely elucidated, cytokine-receptor affinity is known to impact signaling through modulation of the stability and kinetics of ternary complex formation. Receptor trafficking also plays an important and likely underappreciated role in the diversification of cytokine bioactivities but it has been challenging to experimentally probe trafficking effects. We also review recent efforts to quantify levels of intracellular signaling components, as second messenger abundance can affect cytokine-induced bioactivities both quantitatively and qualitatively. We conclude by discussing the application of protein engineering to develop therapeutically relevant cytokines with reduced pleiotropy and redirected biological functionalities.

Type I interferon-mediated pathway interacts with peroxisome proliferator activated receptor-γ (PPAR-γ): at the cross-road of pancreatic cancer cell proliferation

Pancreatic adenocarcinoma remains an unresolved therapeutic challenge because of its intrinsically refractoriness to both chemo- and radiotherapy due to the complexity of signaling and the activation of survival pathways in cancer cells. Recent studies have demonstrated that the combination of some drugs, targeting most of aberrant pathways crucial for the survival of pancreatic cancer cells may be a valid antitumor strategy for this cancer. Type I interferons (IFNs) may have a role in the pathogenesis and progression of pancreatic adenocarcinoma, but the limit of their clinical use is due to the activation of tumor resistance mechanisms, including JAK-2/STAT-3 pathway. Moreover, aberrant constitutive activation of STAT-3 proteins has been frequently detected in pancreatic adenocarcinoma. The selective targeting of these cell survival cascades could be a promising strategy in order to enhance the antitumor effects of type I IFNs. The activation of peroxisome proliferator-activated receptor γ (PPAR-γ), on the other hand, has a suppressive activity on STAT-3. In fact, PPAR-γ agonists negatively modulate STAT-3 through direct and/or indirect mechanisms in several normal and cancer models. This review provides an overview on the current knowledge about the molecular mechanisms and antitumor activity of these two promising classes of drugs for pancreatic cancer therapy. Finally, the synergistic antiproliferative activity of combined IFN-β and troglitazone treatment on pancreatic cancer cell lines, evaluated in vitro, and the consequent potential clinical applications will be discussed.

Ligand-independent interaction of the type I interferon receptor complex is necessary to observe its biological activity

Ectopic coexpression of the two chains of the Type I and Type III interferon (IFN) receptor complexes (IFN-αR1 and IFN-αR2c, or IFN-λR1 and IL-10R2) yielded sensitivity to IFN-alpha or IFN-lambda in only some cells. We found that IFN-αR1 and IFN-αR2c exhibit FRET only when expressed at equivalent and low levels. Expanded clonal cell lines expressing both IFN-αR1 and IFN-αR2c were sensitive to IFN-alpha only when IFN-αR1 and IFN-αR2c exhibited FRET in the absence of human IFN-alpha. Coexpression of RACK-1 or Jak1 enhanced the affinity of the interaction between IFN-αR1 and IFN-αR2c. Both IFN-αR1 and IFN-αR2c exhibited FRET with Jak1 and Tyk2. Together with data showing that disruption of the preassociation between the IFN-gamma receptor chains inhibited its biological activity, we propose that biologically active IFN receptors require ligand-independent juxtaposition of IFN receptor chains assisted by their associated cytosolic proteins.

USP18 establishes the transcriptional and anti-proliferative interferon α/β differential

Type I IFNs (interferons) are pathogen-induced immunoregulatory cytokines that exert anti-viral and anti-proliferative activities through binding to a common cell-surface receptor. Among the 17 human IFN subtypes, IFNβ binds the IFNAR (IFNα receptor) 1/IFNAR2 receptor chains with particularly high affinity and is especially potent in select bioactivities (e.g. anti-proliferative and pro-apoptotic) when compared with IFNα2. However, no molecular basis has been ascribed to this differential action, since the two ligands are equipotent in immediate early signalling events. In the present study we report that IFNβ induces Stat (signal transducer and activator of transcription) phosphorylation and transcriptional activation of ISGs (interferon-stimulated genes), including two genes with pro-apoptotic functions, for a considerably longer time frame than does IFNα2. We show that the diversification of α2/β responses progressively builds up at the receptor level as a result of accumulating USP18 (ubiquitin specific protease 18), itself an ISG, which exerts its negative feedback action by taking advantage of the weakness of IFNα2 binding to the receptor. This represents a novel type of signalling regulation that diversifies the biological potential of IFNs α and β.

Down-regulation of cyclin E1 expression by microRNA-195 accounts for interferon-β-induced inhibition of hepatic stellate cell proliferation

Recent studies have suggested that interferons (IFNs) have an antifibrotic effect in the liver independent of their antiviral effect although its detailed mechanism remains largely unknown. Some microRNAs have been reported to regulate pathophysiological activities of hepatic stellate cells (HSCs). We performed analyses of the antiproliferative effects of IFNs in HSCs with special regard to microRNA-195 (miR-195). We found that miR-195 was prominently down-regulated in the proliferative phase of primary-cultured mouse HSCs. Supporting this fact, IFN-β induced miR-195 expression and inhibited the cell proliferation by delaying their G1 to S phase cell cycle progression in human HSC line LX-2. IFN-β down-regulated cyclin E1 and up-regulated p21 mRNA levels in LX-2 cells. Luciferase reporter assay revealed the direct interaction of miR-195 with the cyclin E1 3'UTR. Overexpression of miR-195 lowered cyclin E1 mRNA and protein expression levels, increased p21 mRNA and protein expression levels, and inhibited cell proliferation in LX-2 cells. Moreover miR-195 inhibition restored cyclin E1 levels that were down-regulated by IFN-β. In conclusion, IFN-β inhibited the proliferation of LX-2 cells by delaying cell cycle progression in G1 to S phase, partially through the down-regulation of cyclin E1 and up-regulation of p21. IFN-induced miR-195 was involved in these processes. These observations reveal a new mechanistic aspect of the antifibrotic effect of IFNs in the liver.

Response of pancreatic cancer cells treated with interferon-alpha or beta and co-exposed to ionising radiation

PURPOSE

Clinical trials on pancreatic cancer demonstrated that interferons (IFN) improve the therapeutic index of combined radio- and chemotherapy. This is believed to be due to radiosensitisation of cells, which, however, needs experimental verification.

MATERIALS AND METHODS

Here, we compared the survival response of ten pancreatic tumour cell lines following ionising radiation (IR), interferon-alpha (IFN-alpha), interferon-beta (IFN-beta) and combined treatment. The effect of combination treatment on apoptosis induction was also determined.

RESULTS

In most cell lines IFN treatment on its own exerted cytotoxicity, which was independent of the expression level of the IFN receptor on the cell surface. Three cell lines showed a radiosensitisation effect while two showed radioprotection. Although IFN-alpha is commonly used in the clinic, IFN-beta induced a stronger cytotoxic response than IFN-alpha in vitro. The likely mechanism of enhancement of radiosensitivity in the responsive cell lines was shown to be an increase of the radiation-induced apoptotic response by IFN pretreatment.

CONCLUSIONS

Given that the in vitro data do not conform to the impressive clinical results observed after combined radio- and chemotherapy with IFN-alpha, it is reasonable to conclude that the sensitising effect of IFN is not mediated through modulating the intrinsic radiosensitivity of pancreatic cancer cells.

Biologic therapy for rheumatoid arthritis: clinical efficacy and predictors of response

We present evidence of a link between interferonβ-1b (IFN-β) and G-protein signaling by demonstrating that IFN-β can induce the expression of the negative regulator of G-protein signaling 1 (RGS1). RGS1 reduces G-protein activation and immune cell migration by interacting with heterotrimeric G-proteins and enhancing their intrinsic GTPase activity. In this study, IFN-β treatment resulted in the induction of RGS1 in peripheral blood mononuclear cells (PBMCs), monocytes, T cells, and B cells. Induction of RGS1 by IFN-β was concentration dependent and observed at both the RNA and protein level. Other members of the RGS family were not induced by IFN-β, and induction of RGS1 required the activation of the IFN receptor. In addition, RGS1 induction was observed in PBMCs obtained from IFN-β-treated multiple sclerosis patients suggesting a possible, as yet unexplored, involvement of G-protein regulation in disease treatment. The upregulation of RGS1 by IFN-β has not been previously reported.

Longitudinal system-based analysis of transcriptional responses to type I interferons

Type I interferons (IFNs) are pleiotropic cytokines that modulate both innate and adaptive immune responses. They have been used to treat autoimmune disorders, cancers, and viral infection and have been demonstrated to elicit differential responses within cells, despite sharing a single receptor. The molecular basis for such differential responses has remained elusive. To identify the mechanisms underlying differential type I IFN signaling, we used whole genome microarrays to measure longitudinal transcriptional events within human CD4(+) T cells treated with IFN-alpha(2b) or IFN-beta(1a). We identified differentially regulated genes, analyzed them for the enrichment of known promoter elements and pathways, and constructed a network module based on weighted gene coexpression network analysis (WGCNA). WGCNA uses advanced statistical measures to find interconnected modules of correlated genes. Overall, differential responses to IFN in CD4(+) T cells related to three dominant themes: migration, antigen presentation, and the cytotoxic response. For migration, WGCNA identified subtype-specific regulation of pre-mRNA processing factor 4 homolog B and eukaryotic translation initiation factor 4A2, which work at various levels within the cell to affect the expression of the chemokine CCL5. WGCNA also identified sterile alpha-motif domain-containing 9-like (SAMD9L) as critical in subtype-independent effects of IFN treatment. RNA interference of SAMD9L expression enhanced the migratory phenotype of activated T cells treated with IFN-beta compared with controls. Through the analysis of the dynamic transcriptional events after differential IFN treatment, we were able to identify specific signatures and to uncover novel genes that may underpin the type I IFN response.

Effects of type I interferons on IGF-mediated autocrine/paracrine growth of human neuroendocrine tumor cells

We recently demonstrated that interferon (IFN)-beta has a more potent antitumor activity than IFN-alpha in BON cells, a neuroendocrine tumor (NET) cell line. The present study showed the role of type I IFNs in the modulation of the insulin-like growth factor (IGF) system in NETs. BON cells expressed IGF-I, IGF-II, IGF-I receptor, and insulin receptor mRNA. In addition, IGF-I and IGF-II stimulated the proliferation of BON cells and induced an inhibition of DNA fragmentation (apoptosis). As evaluated by quantitative RT-PCR, treatment with IFN-alpha (100 IU/ml) or IFN-beta (100 IU/ml) inhibited the expression of IGF-II mRNA (-42% and -65%, respectively, both P < 0.001), whereas IGF-I receptor mRNA was significantly upregulated by IFN-alpha (+28%, P < 0.001) and downregulated by IFN-beta (-47%, P < 0.001). Immunoreactive IGF-II concentration decreased in the conditioned medium during IFN-alpha (-16%, P < 0.05) and IFN-beta (-69%, P < 0.001) treatment. Additionally, IGF-I receptor bioactivity was reduced (-54%) after IFN-beta treatment. Scatchard analysis of (125)I-labeled IGF-I binding to cell membrane of BON cells revealed a dramatic suppression of maximum binding capacity only in the presence of IFN-beta. Finally, the proapoptotic activity of IFN-beta was partially counteracted by the coadministration of IGF-I and IGF-II (both at 50 nM). In conclusion, these data demonstrate that the IGF system has an important role in autocrine/paracrine growth of BON cells. The more potent antitumor activity of IFN-beta compared with IFN-alpha could be explained by several effects on this system: 1) both IFNs inhibit the transcription of IGF-II, but the suppression is significantly higher after IFN-beta than IFN-alpha and 2) only IFN-beta inhibits the expression of IGF-I receptor.

Ligand binding induces a conformational change in ifnar1 that is propagated to its membrane-proximal domain

The type I interferon (IFN) receptor plays a key role in innate immunity against viral and bacterial infections. Here, we show by intramolecular Förster resonance energy transfer spectroscopy that ligand binding induces substantial conformational changes in the ectodomain of ifnar1 (ifnar1-EC). Binding of IFN alpha 2 and IFN beta induce very similar conformations of ifnar1, which were confirmed by single-particle electron microscopy analysis of the ternary complexes formed by IFN alpha 2 or IFN beta with the two receptor subunits ifnar1-EC and ifnar2-EC. Photo-induced electron-transfer-based fluorescence quenching and single-molecule fluorescence lifetime measurements revealed that the ligand-induced conformational change in the membrane-distal domains of ifnar1-EC is propagated to its membrane-proximal domain, which is not involved in ligand recognition but is essential for signal activation. Temperature-dependent ligand binding studies as well as stopped-flow fluorescence experiments corroborated a multistep conformational change in ifnar1 upon ligand binding. Our results thus suggest that the relatively intricate architecture of the type I IFN receptor complex is designed to propagate the ligand binding event to and possibly even across the membrane by conformational changes.

Requirement of catalytically active Tyk2 and accessory signals for the induction of TRAIL mRNA by IFN-beta

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand/Apo2 ligand (TRAIL/Apo2L) mRNA was induced preferentially by interferon (IFN)-beta but not IFN-alpha in human fibrosarcoma and primary fibroblast cells. To characterize the signaling components mediating the IFN subtype-specific induction of this gene, we used mutant cell lines lacking individual components involved in signaling by type I IFNs. TRAIL was not induced by IFN-beta in mutant cell lines U2A, U3A, U4A, U5A, and U6A, which lack, respectively, IFN regulatory factor-9 (IRF-9), Stat1, Jak1, IFNAR-2.2, and Stat2, indicating transcription factor IFN-stimulated gene factor 3 (ISGF3) was essential for the induction of this gene. TRAIL was not induced by IFN-beta in U1A (Tyk2 null) or U1A.R930 cells (that express a kinase-deficient point mutant of Tyk2) but was induced in U1A.wt-5 cells (U1A cells expressing wild-type Tyk2), indicating that Tyk2 protein and kinase activity were both required for induction of the gene. Biochemical and genetic analyses revealed the requirement of transcription factor NF-kappa B and phosphoinositide 3-kinase (PI3K) but not extracellular signal-regulated kinase (ERK) for the induction of TRAIL by IFN-beta. Furthermore, the antiproliferative but not antiviral effects of IFN-beta required catalytically active Tyk2, suggesting that expression of genes, such as TRAIL, may play an important role in mediating the biologic effects of IFNs.

Comparable potency of IFNalpha2 and IFNbeta on immediate JAK/STAT activation but differential down-regulation of IFNAR2

Type I IFNs (interferons) (IFNalpha/beta) form a family of related cytokines that control a variety of cellular functions through binding to a receptor composed of IFNAR (IFNalpha receptor subunit) 1 and 2. Among type I IFNs, the alpha2 and beta subtypes exhibit a large difference in their binding affinities to IFNAR1, and it was suggested that high concentrations of IFNAR1 may compensate for its low intrinsic binding affinity for IFNalpha2. We tested whether receptor-proximal signalling events are sensitive to IFNAR1 surface concentration by investigating the relationship between relative IFNAR1/IFNAR2 surface levels and IFNalpha2 and IFNbeta signalling potencies in several cell lines. For this, we monitored the activation profile of JAK (Janus kinase)/STAT (signal transducer and activator of transcription) proteins, measured basal and ligand-induced surface decay of each receptor subunit and tested the effect of variable IFNAR1 levels on IFNalpha2 signalling potency. Our data show that the cell-surface IFNAR1 level is indeed a limiting factor for assembly of the functional complex, but an increased concentration of it does not translate into an IFNalpha/beta differential JAK/STAT signalling nor does it change the dynamics of the engaged receptor. Importantly, however, our data highlight a differential effect upon routing of IFNAR2. Following binding of IFNalpha2, IFNAR2 is internalized, but, instead of being routed towards degradation as it is when complexed to IFNbeta, it recycles back to the cell surface. These observations suggest strongly that the stability and the intracellular lifetime of the ternary complex account for the differential control of IFNAR2. Moreover, the present study opens up the attractive possibility that endosomal-initiated signalling may contribute to IFNalpha/beta differential bioactivities.

SOCS1 silencing enhances antitumor activity of type I IFNs by regulating apoptosis in neuroendocrine tumor cells

IFN-alpha is commonly used for biotherapy of neuroendocrine carcinomas. However, its antitumor efficacy is often limited due to IFN resistance. In this study, we evaluate the role of suppressor of cytokine signaling protein 1 (SOCS1) in modulating the effects of type I IFNs (IFN-alpha and IFN-beta) in human neuroendocrine BON1 and CM tumor cells. In both cell lines, type I IFNs activated signal transducers and activators of transcription (STAT) and significantly decreased cell viability. However, the effects of IFN-beta were significantly more pronounced than those of IFN-alpha and involved the induction of the intrinsic apoptotic pathway as shown by cleavage of caspase-8, Bid, and caspase-9. Stable overexpression of SOCS1 completely abolished the apoptotic effects of both type I IFNs. In contrast, small interfering RNA (siRNA)-mediated silencing of SOCS1 resulted in strongly enhanced type I IFN signaling as shown by increased and prolonged STAT phosphorylation and stronger induction of apoptosis. Silencing of SOCS1 was associated with down-regulation of basal Bcl-2 and Bcl-xL and up-regulation of basal Bak and Bax, suggesting that reduced SOCS1 expression might lower the threshold of susceptibility to type I IFN-mediated apoptosis by decreasing the ratio of antiapoptotic to proapoptotic molecules. In summary, our results indicate an important role of SOCS1 in IFN resistance of neuroendocrine tumor cells, mediated through negative regulation of type I IFN-induced Jak/STAT signaling. Knocking down SOCS1 by siRNA is a promising new approach to enhance the therapeutic potency of type I IFNs in neuroendocrine tumors.

Antiviral and myocyte protective effects of murine interferon-β and -α2in coxsackievirus B3-induced myocarditis and epicarditis in Balb/c mice

The present study tested the hypothesis that murine (m)IFN-β or mIFN-α2can eliminate cardiac viral load and protect cardiomyocytes from injury in animals infected with coxsackievirus B3 (CVB3). CVB3-inoculated male Balb/c mice exhibited signs of illness, including lethargy, progressive weight loss, and death (10% on day 3 and 100% on day 8). Cardiac viral load was high [4,277 ± 1,009 plaque-forming units and 25 ± 5 copies CVB3/hypoxanthine guanine phosphoribosyl transferase 1 mRNA] on day 4. The cardiac tissue exhibited severe inflammatory infiltration and myocyte damage with an average myocarditis integrated pathology score of 2.1 ± 0.2 on day 7. Most of the mice infected with CVB3 also developed epicarditis, and 55% had intraventricular thrombi present. Treatment with mIFN-β [2.5 to 10 million international units (MIU)/kg] dose-dependently improved the general health status in CVB3-inoculated mice, as evidenced by reduction in weight loss, prevention of death, elimination of cardiac viral load, protection of myocytes from injury, decrease in inflammatory cell infiltration, and attenuation of intraventricular thrombus formation. Treatment with 10 MIU/kg mIFN-α2resulted in a similar level of efficacy as that induced by 5 MIU/kg mIFN-β, with the exception that mIFN-α2did not reduce cardiac CVB3 mRNA. However, mIFN-α2, but not any dose group of mIFN-β, significantly attenuated CVB3-induced epicarditis. These data demonstrate antiviral effects for both mIFN-β and mIFN-α2, which lead to protection of the mice from CVB3-induced myocarditis. However, the potential mechanisms leading to a differential host response for the two isoforms of mIFN remain to be elucidated.

Interferon receptor expression in multiple sclerosis patients

To determine the gene expression of IFNAR1, IFNAR2 and MxA protein and the association with IFNbeta treatment response in MS patients. MS patients treated with IFNbeta had a significant decrease in IFNAR1 and IFNAR2 expression, and a significant increase in MxA compared to non-treated patients and healthy controls. Also, those patients who had a good response to treatment had a significant decrease in IFNAR1 and IFNAR2 expression compared to non-responders, non-treated patients and healthy controls. IFNbeta influences the expression of its receptors, and is greater in patients who respond to IFNbeta treatment. This down-regulation could be indicative of the response to IFNbeta.

Differential receptor subunit affinities of type I interferons govern differential signal activation

Type I interferons (IFNs) elicit antiviral, antiproliferative and immunmodulatory responses by binding to a shared cell surface receptor comprising the transmembrane proteins ifnar1 and ifnar2. Activation of differential response patterns by IFNs has been observed, suggesting that members of the family play different roles in innate immunity. The molecular basis for differential signaling has not been identified yet. Here, we have investigated the recognition of various IFNs including several human IFNalpha species, human IFNomega and human IFNbeta as well as ovine IFNtau2 by the receptor subunits in detail. Binding to the extracellular domains of ifnar1 (ifnar1-EC) and ifnar2 (ifnar2-EC) was monitored in real time by reflectance interference and total internal reflection fluorescence spectroscopy. For all IFNs investigated, competitive 1:1 interaction not only with ifnar2-EC but also with ifnar1-EC was shown. Furthermore, ternary complex formation was studied with ifnar1-EC and ifnar2-EC tethered onto solid-supported membranes. These analyses confirmed that the signaling complexes recruited by IFNs have very similar architectures. However, differences in rate and affinity constants over several orders of magnitude were observed for both the interactions with ifnar1-EC and ifnar2-EC. These data were correlated with the potencies of ISGF3 activation, antiviral and anti-proliferative activity on 2fTGH cells. The ISGF3 formation and antiviral activity correlated very well with the binding affinity towards ifnar2. In contrast, the affinity towards ifnar1 played a key role for antiproliferative activity. A striking correlation was observed for relative binding affinities towards ifnar1 and ifnar2 with the differential antiproliferative potency. This correlation was confirmed by systematically engineering IFNalpha2 mutants with very high differential antiproliferative potency.

Potent inhibitory effects of type I interferons on human adrenocortical carcinoma cell growth

CONTEXT

Adrenocortical carcinoma (ACC) is a rare tumor with a poor prognosis. Despite efforts to develop new therapeutic regimens for metastatic ACC, surgery remains the mainstay of treatment. Interferons are known to exert tumor-suppressive effects in several types of human cancer.

DESIGN

We evaluated the tumor-suppressive effects of type I interferons (IFN)-alpha2b and IFNbeta on the H295 and SW13 human ACC cell lines.

RESULTS

As determined by quantitative RT-PCR analysis and immunocytochemistry, H295 and SW13 cells expressed the active type I IFN receptor (IFNAR) mRNA and protein (IFNAR-1 and IFNAR-2c subunits). Both IFNalpha2b and IFNbeta1a significantly inhibited ACC cell growth in a dose-dependent manner, but the effect of IFNbeta1a (IC50 5 IU/ml, maximal inhibition 96% in H295; IC50 18 IU/ml, maximal inhibition 85% in SW13) was significantly more potent, compared with that of IFNalpha2b (IC50 57 IU/ml, maximal inhibition 35% in H295; IC50 221 IU/ml, maximal inhibition 60% in SW13). Whereas in H295 cells both IFNs induced apoptosis and accumulation of the cells in S phase, the antitumor mechanism in SW13 cells involved cell cycle arrest only. Inhibitors of caspase-3, caspase-8, and caspase-9 counteracted the apoptosis-inducing effect by IFNbeta1a in H295 cells. In H295 cells, IFNbeta1a, but not IFNalpha2b, also strongly suppressed the IGF-II mRNA expression, an important growth factor and hallmark in ACC.

CONCLUSIONS

IFNbeta1a is much more potent than IFNalpha2b to suppress ACC cell proliferation in vitro by induction of apoptosis and cell cycle arrest. Further studies are required to evaluate the potency of IFNbeta1a to inhibit tumor growth in vivo.

Determination of the human type I interferon receptor binding site on human interferon-alpha2 by cross saturation and an NMR-based model of the complex

Type I interferons (IFNs) are a family of homologous helical cytokines that exhibit pleiotropic effects on a wide variety of cell types, including antiviral activity and antibacterial, antiprozoal, immunomodulatory, and cell growth regulatory functions. Consequently, IFNs are the human proteins most widely used in the treatment of several kinds of cancer, hepatitis C, and multiple sclerosis. All type I IFNs bind to a cell surface receptor consisting of two subunits, IFNAR1 and IFNAR2, associating upon binding of interferon. The structure of the extracellular domain of IFNAR2 (R2-EC) was solved recently. Here we study the complex and the binding interface of IFNalpha2 with R2-EC using multidimensional NMR techniques. NMR shows that IFNalpha2 does not undergo significant structural changes upon binding to its receptor, suggesting a lock-and-key mechanism for binding. Cross saturation experiments were used to determine the receptor binding site upon IFNalpha2. The NMR data and previously published mutagenesis data were used to derive a docking model of the complex with an RMSD of 1 Angstrom, and its well-defined orientation between IFNalpha2 and R2-EC and the structural quality greatly improve upon previously suggested models. The relative ligand-receptor orientation is believed to be important for interferon signaling and possibly one of the parameters that distinguish the different IFN I subtypes. This structural information provides important insight into interferon signaling processes and may allow improvement in the development of therapeutically used IFNs and IFN-like molecules.

Complex Modulation of Cell Type-Specific Signaling in Response to Type I Interferons

The type I interferons (IFNs) are pleiotropic cytokines that regulate many different cellular functions. The major signaling pathway activated by type I IFNs involves sequential phosphorylation of the tyrosine residues of the Janus kinase (JAK) and signal transducers and activators of transcription (STAT) proteins, providing the primary mechanism through which gene expression is induced. Recent work has shown that the responses are quite complex, as shown by different responses to specific subtypes of type I IFN, activation of kinases in addition to JAKs, patterns of activation of all seven STATs in different cells, and activation of transcription factors other than STATs. The type I IFNs use this complexity to regulate many different biological functions in different types of cells, by activating different specific signals and patterns of gene expression.

Regulation of apoptosis and proliferation in Ewing's sarcoma--opportunities for targeted therapy

The Ewing's sarcoma family of tumors are malignant tumors of bone and soft tissue which occur predominantely in children and adolescents. Whereas cure rates for patients with localized tumors are around 70%, survival rates for patients with metastases or relapse are poor in spite of intensive chemo- and radiation therapy, demonstrating a clear need for new, more effective therapies. Insights into the biology of the tumors of the Ewing's sarcoma family with identification of the EWS/ETS gene rearrangement as the key event in malignant transformation and its influence on the regulation of various pathways involved in proliferation, differentiation and apoptosis has led to the identification of potential targets for the development of new molecular therapeutics. This review will focus on the regulation of major pathways of proliferation and apoptosis in tumors of the Ewing's sarcoma family and point out how modulation of these pathways might be of potential use for future therapy.

Inquiring into the differential action of interferons (IFNs): an IFN-alpha2 mutant with enhanced affinity to IFNAR1 is functionally similar to IFN-beta

Alpha and beta interferons (IFN-alpha and IFN-beta) are multifunctional cytokines that exhibit differential activities through a common receptor composed of the subunits IFNAR1 and IFNAR2. Here we combined biophysical and functional studies to explore the mechanism that allows the alpha and beta IFNs to act differentially. For this purpose, we have engineered an IFN-alpha2 triple mutant termed the HEQ mutant that mimics the biological properties of IFN-beta. Compared to wild-type (wt) IFN-alpha2, the HEQ mutant confers a 30-fold higher binding affinity towards IFNAR1, comparable to that measured for IFN-beta, resulting in a much higher stability of the ternary complex as measured on model membranes. The HEQ mutant, like IFN-beta, promotes a differentially higher antiproliferative effect than antiviral activity. Both bring on a down-regulation of the IFNAR2 receptor upon induction, confirming an increased ternary complex stability of the plasma membrane. Oligonucleotide microarray experiments showed similar gene transcription profiles induced by the HEQ mutant and IFN-beta and higher levels of gene induction or repression than those for wt IFN-alpha2. Thus, we show that the differential activities of IFN-beta are directly related to the binding affinity for IFNAR1. Conservation of the residues mutated in the HEQ mutant within IFN-alpha subtypes suggests that IFN-alpha has evolved to bind IFNAR1 weakly, apparently to sustain differential levels of biological activities compared to those induced by IFN-beta.

Alternative and accessory pathways in the regulation of IFN-beta-mediated gene expression

Type I interferons (IFNs) induce the transcription of IFN-stimulated genes (ISGs) through activation of the Jak-Stat pathway. Although some determinants of specificity are dictated by the Jak-Stat components, recent observations indicate that the system incorporates other components for selectivity and flexibility, whose mechanisms remain to be defined. We identified a gene, beta-R1, which was induced relatively selectively by IFN-beta as compared with numerous IFN-alpha subtypes. Because all type I IFNs equally activate Jak-Stat signaling to IFN-stimulated gene factor 3 (ISGF3), this observation implied the existence of accessory signals for IFN-induced gene expression. We have used beta-R1 as a model system to examine this accessory signaling. In addition to Jak-Stat signaling for mediating IFN-induced cellular responses, p38 mitogen-activated protein kinase (p38 MAPK), phosphoinositol 3-kinase (PI3K), the IkappaB kinases (IKKs), and nuclear factor-kappaB (NF-kappaB) are some of the accessory components identified as required for the induction of certain IFN-beta-induced genes. This review focuses on the roles of accessory components in IFN-beta-mediated signaling, mechanisms of accessory signal generation, and how they modulate gene induction.

IFN-beta is a highly potent inhibitor of gastroenteropancreatic neuroendocrine tumor cell growth in vitro

IFN-alpha controls hormone secretion and symptoms in human gastroenteropancreatic neuroendocrine tumors (GEP-NET) but it rarely induces a measurable tumor size reduction. The effect of other type I IFNs, e.g., IFN-beta, has not been evaluated. We compared the antitumor effects of IFN-alpha and IFN-beta in BON cells, a functioning human GEP-NET cell line. As determined by quantitative reverse transcription-PCR analysis and immunocytochemistry, BON cells expressed the active type I IFN receptor mRNA and protein (IFNAR-1 and IFNAR-2c subunits). After 3 and 6 days of treatment, IFN-beta significantly inhibited BON cell growth in a time- and dose-dependent manner. IC50 and maximal inhibitory effect on day 6 were 8 IU/mL and 98%, respectively. In contrast, the effect of IFN-alpha resulted significantly in a less potent effect (IC50: 44 IU/mL, maximal inhibition: 26%). IFN-alpha induced only cell cycle arrest, with an accumulation of the cells in S phase. IFN-beta, apart from a more potent delay in S-G2-M phase transit of the cell cycle, also induced a strong stimulation of apoptosis, evaluated by flow cytometry (Annexin V and 7-AAD) and measurement of the DNA fragmentation. Besides, only IFN-beta severely suppressed chromogranin A levels in the medium from BON cells after 6 days of treatment. In conclusion, IFN-beta is much more potent, compared with IFN-alpha, in its inhibitory effect on GEP-NET cell proliferation in vitro through the induction of apoptosis and cell cycle arrest. Further studies are required to establish whether IFN-beta has comparable potent tumor growth inhibitory effects in vivo.

IFN-zeta/ limitin: a member of type I IFN with mild lympho-myelosuppression

Interferon (IFN)-Zeta/limitin has been considered as a novel type I IFN by the Nomenclature Committee of the International Society for Interferon and Cytokine Research. IFN-Zeta/limitin shows some sequence homology with IFN-alpha and IFN-beta, has a globular structure with five alpha-helices and four loops, and recognizes IFN-alpha/beta receptor. Although IFN-zeta/limitin displays antiviral, immunomodulatory, and antitumor effects, it has much less lympho-myelosuppressive activities than IFN-alpha. Treatment of cells with type I IFNs induces and/or activates a number of molecules, which regulate cell cycle and apoptosis. It is noteworthy that IFN-zeta/limitin activates the Tyk2-Daxx and Tyk2-Crk pathways weaker than IFN-alpha. Because experiments using antisense oligonucleotides have revealed their essential role in type I IFN-related suppression of lympho-hematopoiesis, little ability of IFN-zeta/limitin to activate the Tyk2-dependent signaling pathway may explain its uniquely narrow range of biological activities. Further analysis of structure-function relationship of type I IFNs will establish an engineered cytokine with useful features of IFN-zeta/limitin.

Functional Cartography of the Ectodomain of the Type I Interferon Receptor Subunit ifnar1

Ligand-induced cross-linking of the type I interferon (IFN) receptor subunits ifnar1 and ifnar2 induces a pleiotrophic cellular response. Several studies have suggested differential signal activation by flexible recruitment of the accessory receptor subunit ifnar1. We have characterized the roles of the four Ig-like sub-domains (SDs) of the extracellular domain of ifnar1 (ifnar1-EC) for ligand recognition and receptor assembling. Various sub-fragments of ifnar1-EC were expressed in insect cells and purified to homogeneity. Solid phase binding assays with the ligands IFN(alpha)2 and IFN(beta) revealed that all three N-terminal SDs were required and sufficient for ligand binding, and that IFN(alpha)2 and IFN(beta) compete for this binding site. Cellular binding assays with different fragments, however, highlighted the key role of the membrane-proximal SD for the formation of an in situ IFN-receptor complex. Even substitution with the corresponding SD from homologous cytokine receptors did not restore high-affinity ligand binding. Receptor assembling analysis on supported lipid bilayers in vitro revealed that the membrane-proximal SD controls appropriate orientation of the receptor on the membrane, which is required for efficient association of ifnar1 into the ternary complex.

IFNAR1 and IFNAR2 polymorphisms confer susceptibility to multiple sclerosis but not to interferon-beta treatment response

We investigated the role of three polymorphisms in the IFNAR1 (SNPs 18417 and -408) and IFNAR2 (SNP 11876) genes in multiple sclerosis (MS) susceptibility and in the IFNbeta treatment response in a group of 147 patients and 210 controls undergoing interferon therapy during the last 2 years. Only the 18417 and the 11876 SNPs showed an association with disease susceptibility (p=0.001 and 0.035, respectively) although no differential genotype distribution were observed between interferon responders and non-responder MS patients. No alteration of the expression level of IFNAR-1 was observed with respect to the -408 genotypes or to interferon treatment response. These data suggest a role for the IFNAR pathway in susceptibility to MS.

Interferon receptor expression regulates the antiproliferative effects of interferons on cancer cells and solid tumors

In addition to antiviral effects, Type I interferons (IFN) have potent antiproliferative and immunomodulatory activities. Because of these properties IFNs have been evaluated as therapeutics for the treatment of a number of human diseases, including cancer. Currently, IFNs have been shown to be efficacious for the treatment of only a select number of cancers. The reason for this is unclear. Recent evidence has demonstrated that some cancer cell types seem to be defective in their ability to respond to IFN. It has been suggested that defects in IFN signaling is one mechanism by which cancer cells escape responsiveness to Type I IFNs and growth control in general. We report that transfection and enhanced expression of the Type I IFN receptor chain (IFNAR2c) in 3 different human cancer cell lines markedly increases the sensitivity of these cells to the antiproliferative effects of IFNs. In cancer cells transfected with IFNAR2c, dose response curves demonstrate a significant decrease in the concentrations of IFN required to achieve maximum cell death. Furthermore, in these transfected cells, we observe a significant increase in the number of cells undergoing apoptosis, as measured by DNA fragmentation and Caspase 3 activation. In addition, using an in vivo xenograft tumor model we show an increase in the effectiveness of systemically delivered Betaseron in decreasing tumor burden in animals in which solid tumors were generated from IFNAR2c transfected cells. These data show that specific regulation of IFN receptor expression can play a major role in determining the clinical outcome of IFN-based cancer therapeutics by regulating the relative sensitivity of cancer cells to IFN-dependent growth control.

Ligand-induced Assembling of the Type I Interferon Receptor on Supported Lipid Bilayers

Type I interferons (IFNs) elicit antiviral, antiproliferative and immuno-modulatory responses through binding to a shared receptor consisting of the transmembrane proteins ifnar1 and ifnar2. Differential signaling by different interferons, in particular IFNalphas and IFNbeta, suggests different modes of receptor engagement. Using reflectometric interference spectroscopy (RIfS), we studied kinetics and affinities of the interactions between IFNs and the extracellular receptor domains of ifnar1 (ifnar1-EC) and ifnar2 (ifnar2-EC). For IFNalpha2, we determined a K(D) value of 3 nM and 5 microM for the interaction with ifnar2-EC and ifnar1-EC, respectively. As compared to IFNalpha2, IFNbeta formed complexes with ifnar2-EC as well as ifnar1-EC with substantially higher affinity. For neither IFNalpha2 nor IFNbeta was stabilization of the complex with ifnar1-EC in the presence of soluble ifnar2-EC observed. We investigated ligand-induced complex formation with ifnar1-EC and ifnar2-EC being tethered onto solid-supported, fluid lipid bilayers by RIfS and total internal reflection fluorescence spectroscopy. We observed very stable binding of IFNalpha2 at high receptor surface concentrations with an apparent k(d) value approximately 200 times lower than that for ifnar2-EC alone. The apparent k(d) value was strongly dependent on the surface concentration of the receptor components, suggesting kinetic stabilization. This was corroborated by the fast exchange of labeled IFNalpha2 bound to the receptor by unlabeled IFNalpha2. Taken together, our results indicate that IFN first binds to ifnar2 and subsequently recruits ifnar1 in a transient fashion. In particular, this second step is much more efficient for IFNbeta than for IFNalpha2, which could explain differential activities observed for these IFNs.

The p38 mitogen-activated protein kinase pathway and its role in interferon signaling

Interferons (IFNs) are pleiotropic cytokines that exhibit multiple biological effects on cells and tissues. IFN receptors are expressed widely in mammalian cells and virtually all different cell types express them on their surface. The Type I IFN receptor has a multichain structure, composed of at least two distinct receptor subunits, IFNalphaR1 and IFNalphaR2. Two Jak-kinases, Tyk-2 and Jak-1, associate with the different receptor subunits and are activated in response to IFNalpha or IFNbeta to regulate engagement of multiple downstream signaling cascades. These include the Stat-pathway, whose function is essential for transcriptional activation of IFN-sensitive genes, and the insulin receptor substrate pathway, which regulates downstream activation of the phosphatidyl-inositol-3' kinase. Members of the Map family of kinases are also activated by the Type I IFN receptor and participate in the generation of IFN signals. The p38 Map kinase pathway appears to play a very important role in the induction of IFN responses. p38 is rapidly activated during engagement of the Type I IFN receptor, and such an activation is regulated by the small G-protein Rac1, which functions as its upstream effector in a tyrosine kinase-dependent manner. The activated form of p38 regulates downstream activation of other serine kinases, notably MapKapK-2 and MapKapK-3, indicating the existence of Type I IFN-dependent signaling cascades activated downstream of p38. Extensive studies have shown that p38 plays a critical role in Type I IFN-dependent transcriptional regulation, without modifying activation of the Stat-pathway. It is now well established that the function of p38 is essential for gene transcription via ISRE or GAS elements, but has no effects on the phosphorylation of Stat-proteins, the formation of Stat-complexes, and their binding to the promoters of IFN-sensitive genes. As Type I IFNs regulate gene expression for proteins with antiviral properties, it is not surprising that pharmacological inhibition of the p38 pathway blocks induction of IFNalpha-antiviral responses. In addition, pharmacological inhibition of p38 abrogates the suppressive effects of Type I IFNs on normal human hematopoietic progenitors, indicating a critical role for this signaling cascade in the induction of the regulatory effects of Type I IFNs on hematopoiesis. p38 is also activated during IFNalpha-treatment of primary leukemia cells from patients with chronic myelogenous leukemia. Such activation is required for IFNalpha-dependent suppression of leukemic cell progenitor growth, indicating that this pathway plays a critical role in the induction of the antileukemic effects of IFNalpha.

Upregulation of B7 molecules (CD80 and CD86) and exacerbated eosinophilic pulmonary inflammatory response in mice lacking the IFN-beta gene

BACKGROUND

IFN-beta has been shown to be effective as therapy for multiple sclerosis. Some reports attributed its beneficial effects to the capacity to induce a T(H)2 response. However, other studies have suggested that endogenous type I IFN might downregulate the allergic response in mice.

OBJECTIVE

We sought to define the differential role of endogenous IFN-beta in controlling the development of allergic inflammation.

METHODS

We assessed whether deletion of the gene encoding IFN-beta (IFNB) with knockout mice participated in the development of allergic response in ovalbumin (OVA)-sensitized and OVA-challenged mice.

RESULTS

OVA-sensitized and OVA-challenged mice with lack of the IFNB gene had more severe pulmonary inflammation with increased lung local response, including IL-4, IL-5, IL-13, IgE, eosinophilia, and goblet cells, than their litter mates (IFN-beta+/-), whereas no differences were observed in regard to local levels of IFN-gamma. Moreover, systemic response with IgE production is also enhanced. Lack of IFN-beta also results in significantly higher antigen-specific T cells, with higher levels of IL-4, IL-5, and IL-13, whereas no significant differences in IFN-gamma response could be observed. We have also detected a higher ratio of CD4+/CD8+ T cells and increased expression of B7.1/B7.2 on B cells and antigen-presenting cells in IFNB knockout mice.

CONCLUSIONS

These results demonstrate that IFN-beta plays an important role in immunoregulation of allergic response in mice. The stronger pulmonary inflammation could be a consequence of significantly expanded antigen-specific CD4+ T(H)2 cells as a result of efficient antigen presentation by antigen-presenting cells and hence increased production of IgE by B cells.

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.

Different effects of rat interferon alpha, beta and gamma on rat hepatic stellate cell proliferation and activation

BACKGROUND

Liver fibrosis is the common sequel of chronic liver diseases. Recent studies have identified hepatic stellate cells as the primary cell type mediating hepatic fibrogenesis. It has been demonstrated that hepatic stellate cells undergo a process of activation during the development of liver fibrosis. During the activation process, hepatic stellate cells acquire myofibroblast-like phenotype featuring the expression of smooth muscle alpha actin. Interferons have been employed for the treatment of viral hepatitis. However, it is unclear what is the effect of interferons on the prevention and treatment of liver fibrosis. Moreover, it is not clear whether there are any differences among interferon alpha, interferon beta, and interferon gamma in the treatment of liver fibrosis. Therefore, our objective in current study is to investigate the effects of rat interferon-alpha, interferon-beta, and interferon-gamma on the proliferation and activation of rat hepatic stellate cells.

RESULTS

Rat interferon-beta and interferon-gamma significantly inhibited rat hepatic stellate cell proliferation while rat interferon-alpha did not affect the cell proliferation under the same culture condition. Inhibition of cell proliferation was confirmed by both WST-1 cell proliferation assay and 5-bromo-2'-deoxy-uridine incorporation assay. Similar results were observed regarding interferons regulation of hepatic stellate cell activation. Both rat interferon-beta and interferon-gamma reduced smooth muscle alpha-actin abundance after 6 days treatment, but rat interferon-alpha did not alter smooth muscle alpha-actin level.

CONCLUSIONS

Our results indicate that rat interferon-alpha and interferon-beta have different biological effects on rat hepatic stellate cells and suggest that there are different signaling events between interferon-alpha and interferon-beta in hepatic stellate cells.

Stat2 binding to the interferon-alpha receptor 2 subunit is not required for interferon-alpha signaling

The interferon-alpha (IFNalpha) receptor consists of two subunits, the IFNalpha receptor 1 (IFNaR1) and 2 (IFNaR2) chains. Following ligand binding, IFNaR1 is phosphorylated on tyrosine 466, and this site recruits Stat2 via its SH2 domain. In contrast, IFNaR2 binds Stat2 constitutively. In this study we have characterized the Stat2-IFNaR2 interaction and examined its role in IFNalpha signaling. Stat2 binds the major IFNaR2 protein but not a variant containing a shorter cytoplasmic domain. The interaction does not require a STAT SH2 domain. Both tyrosine-phosphorylated and non-phosphorylated Stat2 bind IFNaR2 in vitro; however, relatively little phosphorylated Stat2 associates with IFNaR2 in vivo. In vitro binding assays defined IFNaR2 residues 418-444 as the minimal interaction domain and site-specific mutation of conserved acidic residues within this domain disrupted in vitro and in vivo binding. An IFNaR2 construct carrying these mutations was either (i) overexpressed in 293T cells or (ii) used to complement IFNaR2-deficient U5A cells. Unexpectedly, the activity of an IFNalpha-dependent reporter gene was not reduced but, instead, was enhanced up to 2-fold. This suggests that this particular IFNaR2-Stat2 interaction is not required for IFNalpha signaling, but might act to negatively inhibit signaling. Finally, a doubly truncated recombinant fragment of Stat2, spanning residues 136-702, associated with IFNaR2 in vitro, indicating that the interaction with IFNaR2 is direct and occurs in a central region of Stat2 marked by a hydrophobic core.

Different activities of type I interferons on hepatitis B virus core promoter regulated transcription

The type I interferons (IFNs) are a group of closely related cytokines which have different signal transduction pathways and different biological activities. Using transient transfection of human hepatoma cells with reporter plasmids containing the firefly/renilla luciferase genes under the control of the HBV-Enhancer (Enh) I, Enh II and core promoter we have investigated the biological activities of 10 recombinant (r) type I IFNs on transcription. Low concentrations of IFN (0.025 ng/ml) had a significant and specific inhibitory effect but the potencies of the different recombinant type I IFNs differed markedly with IFNalpha8 and IFNbeta being six-fold more potent than the least effective subtype (IFNalpha1). However, the addition of IFNalpha5-the subtype produced predominantly in the human liver-did not cause any synergistic effects.The non-natural consensus IFN displayed a more pronounced inhibition of HBV-regulated transcription than IFNalpha8 or IFNalpha2 but not IFNbeta. The INF-induced inhibitory effect was not dependent on the presence of the HBV-Enh1 and in particular of an interferon stimulated response element (ISRE)-like sequence. The characterization of different effects among type I interferons on HBV-regulatory elements may implicate an IFN-subtype-specific role for the pathogenesis and treatment of HBV-infection.

Comparison of gene expression patterns induced by treatment of human umbilical vein endothelial cells with IFN-alpha 2b vs. IFN-beta 1a: understanding the functional relationship between distinct type I interferons that act through a common receptor

We analyzed whether interferon-alpha 2b (IFN-alpha 2b) and IFN-beta 1a engage their common receptor to generate activated receptor complexes possessing distinct signaling properties. Human vascular endothelial cells (HUVEC) are 100-1000-fold more sensitive to IFN-beta 1a than to IFN-alpha 2b in in vitro assays. An nonarray-based expression profiling (GeneCalling) technology was employed to compare the patterns and levels of gene expression induced by these IFN as the broadest means by which signaling events could be measured. To distinguish subtype-related differences from dose-related effects, RNA was prepared from HUVEC treated with 50-5000 pg/ml of each IFN. The results showed that at 50 pg/ml IFN, only a subset of the genes induced by IFN-beta 1a were also induced by IFN-alpha 2b and that individual genes were induced to higher levels by IFN-beta 1a. In contrast, at 5000 pg/ml, both subtypes induced essentially identical sets of genes to similar levels of expression. No genes were seen to be induced uniquely by IFN-alpha 2b but not by IFN-beta 1a. The results show that the two IFN are intrinsically capable of inducing similar gene induction responses and do not provide evidence that they generate activated receptor complexes possessing distinct signaling properties. In contrast, the two IFN generate gene induction patterns that are both qualitatively and quantitatively distinct at subsaturating and potentially physiologically more relevant concentrations.

Interferon signaling is dependent on specific tyrosines located within the intracellular domain of IFNAR2c. Expression of IFNAR2c tyrosine mutants in U5A cells

Type I interferons (IFNs) are cytokines that play a central role in mediating antiviral, antiproliferative, and immunomodulatory activities in virtually all cells. These activities are entirely dependent on the interaction of IFNs with their particular cell surface receptor. In this report, we identify two specific tyrosine residues located within the cytoplasmic domain of IFNAR2c that are obligatory for IFN-dependent signaling. Various IFNAR2c tyrosine mutants were expressed in a human lung fibroscarcoma cell line lacking IFNAR2c (U5A). Stable clones expressing these mutants were analyzed for their ability to induce STAT1 and STAT2 activation, ISGF3 transcriptional complex formation, gene expression, and cell growth regulation in response to stimulation with type I IFNs. The replacement of all seven cytoplasmic tyrosine residues of IFNAR2c with phenylalanine resulted in a receptor unable to respond to IFN stimulation. Substitution of single tyrosines at amino acid residue 269, 316, 318, 337, or 512 with phenylalanine had no effect on IFN-dependent signaling, suggesting that no single tyrosine is essential for IFN receptor-mediated signaling. In addition, IFNAR2c retaining five proximal tyrosines residues (269, 306, 316, 318, and 337) or either two distal tyrosine residues (411 or 512) continued to be responsive to IFN stimulation. Surprisingly, the presence of only a single tyrosine at either position 337 or 512 was sufficient to restore a complete IFN response. These results indicate that IFN-dependent signaling proceeds through the redundant usage of two tyrosine residues in the cytoplasmic domain of IFNAR2c.

Receptor for activated C-kinase (RACK-1), a WD motif-containing protein, specifically associates with the human type I IFN receptor

The cytoplasmic domain of the human type I IFN receptor chain 2 (IFNAR2c or IFN-alphaRbetaL) was used as bait in a yeast two-hybrid system to identify novel proteins interacting with this region of the receptor. We report here a specific interaction between the cytoplasmic domain of IFN-alphaRbetaL and a previously identified protein, RACK-1 (receptor for activated C kinase). Using GST fusion proteins encoding different regions of the cytoplasmic domain of IFN-alphaRbetaL, the minimum site for RACK-1 binding was mapped to aa 300-346. RACK-1 binding to IFN-alphaRbetaL did not require the first 91 aa of RACK-1, which includes two WD domains, WD1 and WD2. The interaction between RACK-1 and IFN-alphaRbetaL, but not the human IFN receptor chain 1 (IFNAR1 or IFN-alphaRalpha), was also detected in human Daudi cells by coimmunoprecipitation. RACK-1 was shown to be constitutively associated with IFN-alphaRbetaL, and this association was not effected by stimulation of Daudi cells with type I IFNs (IFN-beta1b). RACK-1 itself did not become tyrosine phosphorylated upon stimulation of Daudi cells with IFN-beta1b. However, stimulation of cells with either IFN-beta1b or PMA did result in an increase in detectable immunofluorescence and intracellular redistribution of RACK-1.

The neutralization of type I IFN biologic actions by anti-IFNAR-2 monoclonal antibodies is not entirely due to inhibition of Jak-Stat tyrosine phosphorylation

A panel of monoclonal antibodies (mAb) derived against human interferon-alpha/beta receptor-2 (IFNAR-2) was evaluated for their ability to antagonize the biologic effects of type 1 interferons (IFN-alpha1, IFN-alpha2a, and IFN-beta). Anti-IFNAR-2 mAb 117.7, 35.9, 53.2, and 51.44 neutralized type I IFN-mediated antiviral, antiproliferative, and major histocompatibility complex (MHC) class I upregulation functions. However, only mAb 51.44 neutralized IFN-alpha2a and IFN-beta-mediated natural killer (NK) cell cytotoxicity. In BIAcore and cell binding studies, only mAb 51.44 and 234.28 inhibited IFN-alpha2a and IFN-beta binding to its receptor. The receptor blockade by mAb 51.44 and 234.28 resulted in the inhibition of IFN-alpha2a and IFN-beta-induced tyrosine phosphorylation of Jak1, Tyk2, Stat1/2/3, and IFNAR-1/2 and inhibition of IFN-stimulated gene factor 3 (ISGF3) formation. mAb 117.7, 35.9, and 53.2, although antagonists of IFN's biologic activities, did not block the binding of IFN-alpha/beta to its receptor. The 117.7 mAb, representative of this class of receptor nonblocking mAb, induced hyper-tyrosine phosphorylation of IFNAR-2 in the presence of IFN-alpha/beta but did not inhibit IFN-alpha/beta-induced Jak-Stat tyrosine phosphorylation and ISGF3 complex formation. These results show that the neutralization of type I IFN biologic actions by anti-IFNAR-2 mAb cannot be entirely explained by inhibition of Jak-Stat tyrosine phosphorylation.

Role of the intracellular domain of the human type I interferon receptor 2 chain (IFNAR2c) in interferon signaling. Expression of IFNAR2c truncation mutants in U5A cells

A human cell line (U5A) lacking the type I interferon (IFN) receptor chain 2 (IFNAR2c) was used to determine the role of the IFNAR2c cytoplasmic domain in regulating IFN-dependent STAT activation, interferon-stimulated gene factor 3 (ISGF3) and c-sis-inducible factor (SIF) complex formation, gene expression, and antiproliferative effects. A panel of U5A cells expressing truncation mutants of IFNAR2c on their cell surface were generated for study. Janus kinase (JAK) activation was detected in all mutant cell lines; however, STAT1 and STAT2 activation was observed only in U5A cells expressing full-length IFNAR2c and IFNAR2c truncated at residue 462 (R2.462). IFNAR2c mutants truncated at residues 417 (R2. 417) and 346 (R2.346) or IFNAR2c mutant lacking tyrosine residues in its cytoplasmic domain (R2.Y-F) render the receptor inactive. A similar pattern was observed for IFN-inducible STAT activation, STAT complex formation, and STAT-DNA binding. Consistent with these data, IFN-inducible gene expression was ablated in U5A, R2.Y-F, R2.417, and R2.346 cell lines. The implications are that tyrosine phosphorylation and the 462-417 region of IFNAR2c are independently obligatory for receptor activation. In addition, the distal 53 amino acids of the intracellular domain of IFNAR2c are not required for IFN-receptor mediated STAT activation, ISFG3 or SIF complex formation, induction of gene expression, and inhibition of thymidine incorporation. These data demonstrate for the first time that both tyrosine phosphorylation and a specific domain of IFNAR2c are required in human cells for IFN-dependent coupling of JAK activation to STAT phosphorylation, gene induction, and antiproliferative effects. In addition, human and murine cells appear to require different regions of the cytoplasmic domain of IFNAR2c for regulation of IFN responses.

IFN-beta induces serine phosphorylation of Stat-1 in Ewing's sarcoma cells and mediates apoptosis via induction of IRF-1 and activation of caspase-7

Four human cell lines derived from Ewing's sarcoma, EW-7, EW-1, COH and ORS, were investigated to establish the effects of human recombinant interferon-alpha2a and human recombinant interferon-beta on cell proliferation and apoptosis. All four cell lines were much more sensitive to the antiproliferative effects of IFN-beta than of IFN-alpha. Analysis of the early signals triggered by IFN-alpha and IFN-beta demonstrated that the two IFNs were similarly effective in inducing tyrosine phosphorylation of the Jak-1 and Tyk-2 kinases and the transcription factors Stat-1 and Stat-2. Interestingly, an additional rapid phosphorylation of Stat-1 on serine was observed after IFN-beta treatment, with concomitant activation of p38 mitogen-activated protein kinase. In these cells, Stat-1 Ser727 phosphorylation in response to IFN-beta was found to be impaired by p38 MAPkinase inhibitor (SB203580). IFN-beta induced the formation of the Interferon Stimulated Gene Factor 3 complex more efficiently than IFN-alpha, as well as sustained induction of IRF-1, which may account for its greater induction of 2'5'oligo(A)synthetase and greater inhibition of cell proliferation. IFN-beta, but not IFN-alpha, induced apoptosis in wild-type p53 EW-7 and COH cell lines, but not in the mutated p53 EW-1 or ORS cell lines. The apoptosis induced by IFN-beta in EW-7 and COH cell lines appeared to be mediated by IRF-1 and involved the activation of caspase-7. Ectopic expression of IRF-1 induced apoptosis in all four cell lines which correlated with the activation of caspase-7 and with the downregulation of the Bcl-2 oncoprotein, as observed for IFN-beta-induced apoptosis in parental EW-7 and COH cell lines.

Development of an Immunofluorometric, High-Capacity, Cell-Based Assay for the Measurement of Human Type I and Type II Interferons

We have developed a cell-based 96-well microtiter plate, high throughput assay for measuring both type I and type II interferon (IFN) activity on human cells. This assay makes use of a previously described IFN-specific reporter stably expressed in human HT 1080 cells. The induction of the reporter by IFN is determined by measuring the IFN-dependent expression of CD2 on the cell surface. The cytokine-induced expression of CD2 occurs within 48 h and is measured using a time-resolved fluorometric immunoassay. The limit of detection for type I IFN is.0.4 IU/ml. Interassay and intraassay coefficients of variation were 1.1% and 1.3% for the medium control (31 IU IFNb1b/ml), respectively. The limit of detection for type II IFN is.8 IU/ml, and the assay coefficients of variation are similar to those determined for type I IFNs. The level of sensitivity for this assay is comparable to other assays commonly used to measure IFN activity on cells. The current assay has an advantage over antiviral and antiproliferative assays, in that there is no requirement for the use of pathogenic virus or for determining viable cell numbers. The current assay is ideally suited for increasing sample screening and high-capacity automation, making it an excellent tool for drug discovery.

Anti-inflammatory action of type I interferons deduced from mice expressing interferon beta

Type I interferons (IFN) are widely used for the therapeutic treatment of viral infections, tumor growth and various chronic diseases such as multiple sclerosis. Antagonism between type I IFNs and IFN-gamma has been described in cells of the immune system, in particular in the activation of macrophages. To study the systemic effects of type I IFNs we used transgenic mice carrying a human IFN-beta (hIFN-beta) gene under the control of the rat insulin I promoter. These animals expressed high levels of hIFN-beta in beta-pancreatic cells, and the ability of the macrophages to respond to pro-inflammatory stimuli was analyzed. Transgenic mice exhibited an increased extravasation of cells to the peritoneal cavity after eliciting with thioglycollate broth. The expression of the inducible form of nitric oxide synthase and cyclooxygenase-2, two enzymes involved in inflammation, was impaired in transgenic animals challenged with lipopolysaccharide and IFN-gamma. Analysis of the mechanisms leading to this attenuated inflammatory response showed a decrease in the serum levels of TNF-alpha and an inhibition of the activation of the transcription factor NF-KB in various tissues. These results indicate that systemic administration of IFN-beta might influence the response to pro-inflammatory stimuli, in particular through the antagonism of IFN-gamma signaling.