Interferon-alpha/beta-receptor interactions: a complex story unfolding

Natural Killer Cell Derived Microvesicles Affect the Function of Trophoblast Cells

The interaction of natural killer (NK) and trophoblast cells underlies the formation of immune tolerance in the mother-fetus system and the maintenance of the physiological course of pregnancy. In addition, NK cells affect the function of trophoblast cells, interacting with them via the receptor apparatus and through the production of cytokines. Microvesicles (MVs) derived from NK cells are able to change the function of target cells. However, in the overall pattern of interactions between NK cells and trophoblasts, the possibility that both can transmit signals to each other via MVs has not been taken into account. Therefore, the aim of this study was to assess the effect of NK cell-derived MVs on the phenotype, proliferation, and migration of trophoblast cells and their expression of intracellular messengers. We carried out assays for the detection of content transferred from MV to trophoblasts. We found that NK cell-derived MVs did not affect the expression of CD54, CD105, CD126, CD130, CD181, CD119, and CD120a receptors in trophoblast cells or lead to the appearance of CD45 and CD56 receptors in the trophoblast membrane. Further, the MVs reduced the proliferation but increased the migration of trophoblasts with no changes to their viability. Incubation of trophoblast cells in the presence of MVs resulted in the activation of STAT3 via pSTAT3(Ser727) but not via pSTAT3(Tyr705). The treatment of trophoblasts with MVs did not result in the phosphorylation of STAT1 and ERK1/2. The obtained data indicate that NK cell-derived MVs influence the function of trophoblast cells, which is accompanied by the activation of STAT3 signaling.

Changes in antibody binding and functionality after humanizing a murine scFv anti-IFN-α2: From in silico studies to experimental analysis

The structural and dynamic changes introduced during antibody humanization continue to be a topic open to new contributions. For this reason, the study of structural and functional changes of a murine scFv (mu.scFv) anti-rhIFN-α2b after humanization was carried out. As it was shown by long molecular dynamics simulations and circular dichroism analysis, changes in primary sequence affected the tertiary structure of the humanized scFv (hz.scFv): the position of the variable domain of light chain (VL) respective to the variable domain of heavy chain (VH) in each scFv molecule was different. This change mainly impacted on conformation and dynamics of the complementarity-determining region 3 of VH (CDR-H3) which led to changes in the specificity and affinity of humanized scFv (hz.scFv). These observations agree with experimental results that showed a decrease in the antigen-binding strength of hz.scFv, and different capacities of these molecules to neutralize the in vitro rhIFN-α2b biological activity. Besides, experimental studies to characterize antigen-antibody binding showed that mu.scFv and hz.scFv bind to the same antigen area and recognize a conformational epitope, which is evidence of docking results. Finally, the differences between these molecules to neutralize the in vitro rhIFN-α2b biological activity were described as a consequence of the blockade of certain functionally relevant amino acids of the cytokine, after scFv binding. All these observations confirmed that humanization affected the affinity and specificity of hz.scFv and pointed out that two specific changes in the frameworks would be responsible.

Immunomodulatory antitumor effect of interferon‑beta combined with gemcitabine in pancreatic cancer

Resistance to gemcitabine is common and critically limits its therapeutic efficacy in patients with pancreatic cancer. Interferon‑beta (IFN‑β) induces numerous antitumor effects and synergizes with gemcitabine treatment. The immunomodulatory effects of this treatment regimen have not yet been described. In the present study, the antitumor effect of IFN‑β combined with gemcitabine was investigated in immune competent mice. Mouse KPC3 cells were used in all experiments. Treatment effects were determined with cell proliferation assay. Reverse transcription‑quantitative PCR was used to measure gene expression. For in vivo experiments, cells were subcutaneously injected in immune competent mice. For immune profiling, NanoString analysis was performed on tumor samples of treated and untreated mice. Baseline expression of Ifnar‑1 and Ifnar‑2c in KPC3 cells was 1.42±0.16 and 1.50±0.17, respectively. IC50 value of IFN‑β on cell growth was high (>1,000 IU/ml). IFN‑β pre‑treatment increased the in vitro response to gemcitabine (1.3‑fold decrease in EC50; P<0.001). In vivo, tumor size was not statistically significant smaller in mice treated with IFN‑β plus gemcitabine (707±92 mm3 vs. 1,239±338 mm3 in vehicle‑treated mice; P=0.16). IFN‑β alone upregulated expression of numerous immune‑related genes. This effect was less pronounced when combined with gemcitabine. For the first time, to the best of our knowledge, the immunomodulatory effects of IFN‑β, alone and combined with gemcitabine, in pancreatic cancer were reported. Prognostic markers for predicting effective responses to IFN‑β therapy are urgently needed.

The Interplay Between Coronavirus and Type I IFN Response

In the past few decades, newly evolved coronaviruses have posed a global threat to public health and animal breeding. To control and prevent the coronavirus-related diseases, understanding the interaction of the coronavirus and the host immune system is the top priority. Coronaviruses have evolved multiple mechanisms to evade or antagonize the host immune response to ensure their replication. As the first line and main component of innate immune response, type I IFN response is able to restrict virus in the initial infection stage; it is thus not surprising that the primary aim of the virus is to evade or antagonize the IFN response. Gaining a profound understanding of the interaction between coronaviruses and type I IFN response will shed light on vaccine development and therapeutics. In this review, we provide an update on the current knowledge on strategies employed by coronaviruses to evade type I IFN response.

Binding of interferon reduces the force of unfolding for interferon receptor 1

Differential signaling of the type I interferon receptor (IFNAR) has been correlated with the ability of its subunit, IFNAR1, to differentially recognize a large spectrum of different ligands, which involves intricate conformational re-arrangements of multiple interacting domains. To shed light onto the structural determinants governing ligand recognition, we compared the force-induced unfolding of the IFNAR1 ectodomain when bound to interferon and when free, using the atomic force microscope and steered molecular dynamics simulations. Unexpectedly, we find that IFNAR1 is easier to mechanically unfold when bound to interferon than when free. Analysis of the structures indicated that the origin of the reduction in unfolding forces is a conformational change in IFNAR1 induced by ligand binding.

Differential Type I Interferon Signaling Is a Master Regulator of Susceptibility to Postinfluenza Bacterial Superinfection

Bacterial superinfections are a primary cause of death during influenza pandemics and epidemics. Type I interferon (IFN) signaling contributes to increased susceptibility of mice to bacterial superinfection around day 7 post-influenza A virus (IAV) infection. Here we demonstrate that the reduced susceptibility to methicillin-resistant Staphylococcus aureus (MRSA) at day 3 post-IAV infection, which we previously reported was due to interleukin-13 (IL-13)/IFN-γ responses, is also dependent on type I IFN signaling and its subsequent requirement for protective IL-13 production. We found, through utilization of blocking antibodies, that reduced susceptibility to MRSA at day 3 post-IAV infection was IFN-β dependent, whereas the increased susceptibility at day 7 was IFN-α dependent. IFN-β signaling early in IAV infection was required for MRSA clearance, whereas IFN-α signaling late in infection was not, though it did mediate increased susceptibility to MRSA at that time. Type I IFN receptor (IFNAR) signaling in CD11c⁺ and Ly6G⁺ cells was required for the observed reduced susceptibility at day 3 post-IAV infection. Depletion of Ly6G⁺ cells in mice in which IFNAR signaling was either blocked or deleted indicated that Ly6G⁺ cells were responsible for the IFNAR signaling-dependent susceptibility to MRSA superinfection at day 7 post-IAV infection. Thus, during IAV infection, the temporal differences in type I IFN signaling increased bactericidal activity of both CD11c⁺ and Ly6G⁺ cells at day 3 and reduced effector function of Ly6G⁺ cells at day 7. The temporal differential outcomes induced by IFN-β (day 3) and IFN-α (day 7) signaling through the same IFNAR resulted in differential susceptibility to MRSA at 3 and 7 days post-IAV infection.

Approximately 114,000 hospitalizations and 40,000 annual deaths in the United States are associated with influenza A virus (IAV) infections. Frequently, these deaths are due to community-acquired Gram-positive bacterial species, many of which show increasing resistance to antibiotic therapy. Severe complications, including parapneumonic empyema and necrotizing pneumonia, can arise, depending on virulence factors expressed by either the virus or bacteria. Unfortunately, we are unable to control the expression of these virulence factors, making host responses a logical target for therapeutic interventions. Moreover, interactions between virus, host, and bacteria that exacerbate IAV-related morbidities and mortalities are largely unknown. Here, we show that type I interferon (IFN) expression can modulate susceptibility to methicillin-resistant Staphylococcus aureus (MRSA) infection, with IFN-β reducing host susceptibility to MRSA infection while IFN-α increases susceptibility. Our data indicate that treatments designed to augment IFN-β and/or inhibit IFN-α production around day 7 post-IAV infection could reduce susceptibility to deadly superinfections.

Receptor dimerization dynamics as a regulatory valve for plasticity of type I interferon signaling

Type I interferons (IFNs) activate differential cellular responses through a shared cell surface receptor composed of the two subunits, IFNAR1 and IFNAR2. We propose here a mechanistic model for how IFN receptor plasticity is regulated on the level of receptor dimerization. Quantitative single-molecule imaging of receptor assembly in the plasma membrane of living cells clearly identified IFN-induced dimerization of IFNAR1 and IFNAR2. The negative feedback regulator ubiquitin-specific protease 18 (USP18) potently interferes with the recruitment of IFNAR1 into the ternary complex, probably by impeding complex stabilization related to the associated Janus kinases. Thus, the responsiveness to IFNα2 is potently down-regulated after the first wave of gene induction, while IFNβ, due to its ∼100-fold higher binding affinity, is still able to efficiently recruit IFNAR1. Consistent with functional data, this novel regulatory mechanism at the level of receptor assembly explains how signaling by IFNβ is maintained over longer times compared with IFNα2 as a temporally encoded cause of functional receptor plasticity.

A novel nuclear trafficking module regulates the nucleocytoplasmic localization of the rabies virus interferon antagonist, P protein

Regulated nucleocytoplasmic transport of proteins is central to cellular function and dysfunction during processes such as viral infection. Active protein trafficking into and out of the nucleus is dependent on the presence within cargo proteins of intrinsic specific modular signals for nuclear import (nuclear localization signals, NLSs) and export (nuclear export signals, NESs). Rabies virus (RabV) phospho (P) protein, which is largely responsible for antagonising the host anti-viral response, is expressed as five isoforms (P1-P5). The subcellular trafficking of these isoforms is thought to depend on a balance between the activities of a dominant N-terminal NES (N-NES) and a distinct C-terminal NLS (C-NLS). Specifically, the N-NES-containing isoforms P1 and P2 are cytoplasmic, whereas the shorter P3-P5 isoforms, which lack the N-NES, are believed to be nuclear through the activity of the C-NLS. Here, we show for the first time that RabV P contains an additional strong NLS in the N-terminal region (N-NLS), which, intriguingly, overlaps with the N-NES. This arrangement represents a novel nuclear trafficking module where the N-NLS is inactive in P1 but becomes activated in P3, concomitant with truncation of the N-NES, to become the principal targeting signal conferring nuclear accumulation. Understanding this unique switch arrangement of overlapping, co-regulated NES/NLS sequences is vital to delineating the critical role of RabV P protein in viral infection.

The yin and yang of viruses and interferons

Interferons (IFNs)-α/β are critical effectors of the innate immune response to virus infections. Through activation of the IFN-α/β receptor (IFNAR), they induce expression of IFN-stimulated genes (ISGs) that encode antiviral proteins capable of suppressing viral replication and promoting viral clearance. Many highly pathogenic viruses have evolved mechanisms to evade an IFN response and the balance between the robustness of the host immune response and viral antagonistic mechanisms determines whether or not the virus is cleared. Here, we discuss IFNs as broad-spectrum antivirals for treatment of acute virus infections. In particular, they are useful for treatment of re-emerging virus infections, where direct-acting antivirals (DAAs) have limited utility due to DAA-resistant mutations, and for newly emerging virus strains in which the time to vaccine availability precludes vaccination at the onset of an outbreak.

Interferon modulates central nervous system function

The interferons (IFNs) are an endogenous pleiotropic family of cytokines that perform fundamental physiological functions as well as protecting host organisms from disease and in maintaining homeostasis. This review covers the effects of endogenous IFN on the nervous system. It starts with the description of its receptors, followed how it modulate neuronal activity, mood, sleep, temperature, the endocrine system, the opioid system and how it regulate food consumption and the immune system. Similar to other multifunctional cytokines, an excessive or inappropriate activity of IFNs can cause toxicity and even death. Furthermore, IFNs are currently the major treatment modality for several malignant and non-malignant diseases such as chronic hepatitis C and B, multiple sclerosis, hematological malignancies, malignant melanoma, renal cell carcinoma, etc.

Beta interferon controls West Nile virus infection and pathogenesis in mice

Studies with mice lacking the common plasma membrane receptor for type I interferon (IFN-αβR(-)(/)(-)) have revealed that IFN signaling restricts tropism, dissemination, and lethality after infection with West Nile virus (WNV) or several other pathogenic viruses. However, the specific functions of individual IFN subtypes remain uncertain. Here, using IFN-β(-)(/)(-) mice, we defined the antiviral and immunomodulatory function of this IFN subtype in restricting viral infection. IFN-β(-)(/)(-) mice were more vulnerable to WNV infection than wild-type mice, succumbing more quickly and with greater overall mortality, although the phenotype was less severe than that of IFN-αβR(-)(/)(-) mice. The increased susceptibility of IFN-β(-)(/)(-) mice was accompanied by enhanced viral replication in different tissues. Consistent with a direct role for IFN-β in control of WNV replication, viral titers in ex vivo cultures of macrophages, dendritic cells, fibroblasts, and cerebellar granule cell neurons, but not cortical neurons, from IFN-β(-)(/)(-) mice were greater than in wild-type cells. Although detailed immunological analysis revealed no major deficits in the quality or quantity of WNV-specific antibodies or CD8(+) T cells, we observed an altered CD4(+) CD25(+) FoxP3(+) regulatory T cell response, with greater numbers after infection. Collectively, these results suggest that IFN-β controls WNV pathogenesis by restricting infection in key cell types and by modulating T cell regulatory networks.

Development of a protein biochip to identify 6 monoclonal antibodies against subtypes of recombinant human interferons

Recombinant human interferons (rhIFNs) are broadly used as effective therapeutic agents with antiviral, antitumor, and immune-modulating properties. Advances in protein biochip technology have benefited the medical community greatly, making true parallelism, miniaturization, and high throughput possible. In this study, 5 rhIFN proteins (IFN-alpha1b, IFN-alpha2a, IFN-alpha2b, IFN-beta, and IFN-gamma) were immobilized onto an N-hydroxysuccinimide (NHS)-modified gold-based biochip. The protein biochip was incubated with 6 specific mouse IgG antibodies (AK1, AK2, AK3, AK4, BK1, and CK1) against the human IFNs and then with Cy3-conjugated goat anti-mouse IgG antibody. The results showed that monoclonal antibody AK1 presented a unique binding characteristic to IFN-alpha1b. AK2 reacted in immunoassays equally with IFN-alpha2a and IFN-alpha2b. AK3 detected IFN-alpha1b, IFN-alpha2a, and IFN-alpha2b. AK4 had positive immunological responses directed to both IFN-alpha1b and IFN-alpha2b. Monoclonal antibodies BK1 and CK1 recognized epitope of IFN-beta and IFN-gamma, specifically. The assay specificity of the biochip was further confirmed by enzyme-linked immunosorbent assay (ELISA) and western blotting. Finally, 88 serum samples from patients treated with rhIFN-alpha2b were simultaneously tested on a single biochip. The result demonstrated that 6.8% (6 of 88 cases) presented positive reactions to anti-IFN-alpha2b antibodies, indicating that the patients under rhIFN-alpha2b therapy produced neutralized antibody against the IFN. The biochip format would offer a competitive alternative tool not only for facilitating characterization of IFN subtypes but also potentially for enabling clinical serum detection of corresponding antibodies directed against IFNs.

Suppression of interferon (IFN)-inducible genes and IFN-mediated functional responses in BCR-ABL-expressing cells

The interferons (IFNs) are cytokines that play key roles in host defense against viral infections and immune surveillance against cancer. We report that BCR-ABL transformation of hematopoietic cells results in suppression of IFN-dependent responses, including transcription of IFN-inducible genes and generation of IFN-mediated antiviral effects. BCR-ABL transformation suppresses expression of several IFN-regulated genes containing IFN-sensitive response element (ISRE) or GAS elements in their promoters, including Isg15, Irf1, Irf9, and Ifit2 (interferon-induced protein with tetratricopeptide repeats 2). Suppression of transcription of ISRE-containing genes is also seen in cells expressing various BCR-ABL kinase domain mutants, including T315I, H396P, Y253F, and E255K, but not kinase-defective BCR-ABL. Such effects are associated with impaired IFN-dependent phosphorylation of Stat1 on Tyr(701) and Stat3 on Tyr(705) and defective binding of Stat complexes to ISRE or GAS elements. Beyond suppression of Stat activities, BCR-ABL inhibits IFN-inducible phosphorylation/activation of the p38 MAPK, suggesting a dual mechanism by which this abnormal fusion protein blocks IFN transcriptional responses. The inhibitory activities of BCR-ABL ultimately result in impaired IFNalpha-mediated protection against encephalomyocarditis virus infection and reversal of IFN-dependent growth suppression. Altogether, our data provide evidence for a novel mechanism by which BCR-ABL impairs host defenses and promotes malignant transformation, involving dual suppression of IFN-activated signaling pathways.

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.

Two interferons alpha influence each other during their interaction with the extracellular domain of human type interferon receptor subunit 2

The interaction between two human interferons alpha (IFN-alphas) and the extracellular (EC) domain of human type I IFN receptor subunit 2 (IFNAR2) was analyzed. Previous experiments using Daudi cells showed that IFN-alpha21b and some IFN-alpha hybrids (made from IFN-alpha2c and 21b) competed poorly for the IFN-alpha2b binding site. This study examined the causes of the poor competition between these IFN-alphas. IFN-alpha2c and the IFN hybrid CM3 {IFN-alpha21b(1-75)(81-95)/IFN-alpha2c(76-80) (96-166), Y86K} were selected for this study based on their cell binding and biological properties. Competitive binding ELISA, native electrophoresis followed by Western blot, electrospray ionization mass spectrometry (ESI-MS), surface plasmon resonance biosensor (SPR) analysis, as well as neutralization of antiproliferative activities on Daudi cells in the presence of soluble IFNAR2-EC show evidence that each of the described IFN-alpha subtypes affected the binding of the other IFN-alpha to IFNAR2-EC by affecting the stability of the complex, i.e., dissociation of the complex. Moreover, native electrophoresis with different IFNAR2-EC mutants showed that IFN-alpha2c and CM3 utilize different amino acids in the binding domain of IFNAR2-EC. In addition to that, analytical ultracentrifugation (AUC) revealed differences in the oligomeric state of the two studied interferons. Our results demonstrated that two individual IFN-alphas interact differentially with IFNAR2-EC and influence each other during this interaction. This study contributes to the understanding of the mutual interaction between multiple IFN-alpha subtypes during the competition for binding to the receptor.

Type I interferons in the treatment of pancreatic cancer: mechanisms of action and role of related receptors

OBJECTIVE

We evaluated the role of type I interferons (IFNs) and IFN receptors in the regulation of cell growth in 3 human pancreatic adenocarcinoma cell lines (BxPC-3, MiaPaCa-2, and Panc-1).

BACKGROUND

Chemotherapy and radiotherapy have a marginal role in the management of pancreatic adenocarcinoma. The addition of IFN-alpha showed promising results in early clinical trials.

METHODS

Cell proliferation and apoptosis were evaluated by DNA measurement and DNA fragmentation, respectively. Type I IFN receptor (IFNAR-1 and IFNAR-2 subunits) was determined by quantitative RT-PCR and immunocytochemistry. Cell cycle distribution was evaluated by propidium iodide staining and flow-cytometric analysis.

RESULTS

The incubation with IFN-beta for 6 days showed a potent inhibitory effect on the proliferation of BxPC-3 (IC(50), 14 IU/mL) and MiaPaCa-2 (IC(50), 64 IU/mL). The inhibitory effect of IFN-beta was stronger than IFN-alpha in all 3 cell lines and mainly modulated by the stimulation of apoptosis, although cell cycle arrest was induced as well. The expression of the type I IFN receptors was significantly higher in BxPC-3 (the most sensitive cell line to IFN) and mainly localized on the membrane, whereas in Panc-1 (the most resistant cell line) about 60% to 70% of cells were negative for IFNAR-2c with a mainly cytoplasmic staining for IFNAR-2c.

CONCLUSION

The antitumor activity of IFN-beta is more potent than IFN-alpha in pancreatic cancer cell lines through the induction of apoptosis. Further studies should investigate in vivo whether the intensity and distribution of IFNAR-1 and IFNAR-2c may predict the response to therapy with IFN-alpha and IFN-beta in pancreatic cancer.

Enhancement of Human Melanoma Antigen Expression by IFN-β

Although many immunotherapeutic investigations have focused on improving the effector limb of the antitumor response, few studies have addressed preventing the loss of tumor-associated Ag (TAA) expression, associated with immune escape by tumors. We found that TAA loss from human melanomas usually results from reversible gene down-regulation, rather than gene deletion or mutation. Previously, we showed that inhibitors of MAPK-signaling pathways up-regulate TAA expression in melanoma cell lines. We have now identified IFN-beta as an additional stimulus to TAA expression, including Melan-A/MART-1, gp100, and MAGE-A1. IFN-beta (but neither IFN-alpha nor IFN-gamma) augmented both protein and mRNA expression of melanocytic TAA in 15 melanoma lines (irrespective of initial Ag-expression levels). Treatment of low Ag melanoma lines with IFN-beta increased expression of melanocyte-lineage Ags, inducing susceptibility to lysis by specific CTLs. Treatment with IFN-beta also enhances expression of class I HLA molecules, thereby inducing both nominal TAA and the presenting HLA molecule. Data from fluorescent cellular reporter systems demonstrated that IFN-beta triggers promoter activation, resulting in augmentation of Ag expression. In addition to enhancing TAA expression in melanomas, IFN-beta also stimulated expression of the melanocytic Ag gp100 in cells of other neural crest-derived tumor lines (gliomas) and certain unrelated tumors. Because IFN-beta is already approved for human clinical use in other contexts, it may prove useful as a cotreatment for augmenting tumor Ag expression during immunotherapy.

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.

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.

Interferons and viruses: signaling for supremacy

Interferon (IFN)-alpha and IFN-beta are critical mediators of host defense against microbial challenges, directly interfering with viral infection and influencing both the innate and adaptive immune responses. IFNs exert their effects in target cells through the activation of a cell-surface receptor, leading to a cascade of signaling events that determine transcriptional and translation regulation. Understanding the circuitry associated with IFN-mediated signal transduction that leads to a specific biological outcome has been a major focus of our laboratory. Through the efforts of graduate students, postdoctoral fellows, a skilled research technologist, and important collaborations with investigators elsewhere, we have provided some insights into the complexity of the IFN system-and the elegance and simplicity of how protein-protein interactions define biological function.

Transformation of mouse fibroblasts alters the induction pattern of type I IFNs after virus infection

Type I interferons (IFNs) have been shown to be involved in many immune defence and inflammatory responses. We here show that IFN-beta plays an absolute essential role in the efficient induction of all type I IFNs after infection of primary embryonic as well as primary adult fibroblasts with Sendai virus. In contrast, after immortalization of such fibroblasts with SV40 large T antigen, IFN-alpha4 can be induced independently of IFN-beta. However, efficient secretion of type I IFNs even in immortalized fibroblasts is only found when the complete signalling loop is induced by IFN-beta.

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.

Diversity and Relatedness Among the Type I Interferons

Type I interferons (IFNs) include the IFN-alpha family of subtypes, IFN-beta, IFN-omega, IFN-tau, IFN-kappa, IFN-lambda, and IFN-zeta. IFN genes lack introns and encode secretory signal peptide sequences that are proteolytically cleaved prior to secretion from the cell. In contrast to the approximately 50% amino acid sequence identity among the human IFN-alpha subtypes, human IFN-alphas share approximately 22% identity with human IFN-beta and 37% identity with human IFN-omega. Many of the conserved residues among the type I IFNs are implicated in receptor recognition and structural integrity. This report provides an update on the gene annotations for the mouse and human IFN gene clusters on chromosome 4 and 9, respectively, with accompanying amino acid sequence alignments. Based on sequence identities, a phylogenic tree analysis for the different mammalian Type I IFNs is also presented, showing the high degree of relatedness among these IFNs. Notably, sequence alignment of the different human and mouse IFN promoter regions reveals different signature patterns for transcription factor binding sites, implying different inducers might differentially activate the transcription of the different IFNs.

NMR backbone dynamics of the human type I interferon binding subunit, a representative cytokine receptor

The antiviral and antiproliferative activities of type I interferons (IFNs) are mediated by a common receptor, and its second subunit (IFNAR2) exhibits nanomolar affinity to both IFNalpha and IFNbeta subtypes. We have previously determined the structure of the IFN-binding extracellular domain of IFNAR2 (IFNAR2-EC) using multidimensional NMR [Chill, J. H., Quadt, S. R., Levy, R., Schreiber, G. E., and Anglister, J. (2003) Structure 11, 791-802], showing it to comprise two fibronectin domains linked by a hinge. As the first cytokine receptor structure determined in the unliganded state and in solution, IFNAR2-EC offers an opportunity to characterize the dynamics of the cytokine receptor family and their correlation to biological function. Backbone dynamics of IFNAR2-EC were investigated using 15N relaxation at 11.74 and 18.79 T, and measurements of residual dipolar couplings (RDCs). Dynamics of the binding site distinguish between rigid structural domains, which stabilize the binding site conformation, and a more flexible binding interface which interacts with the ligand. Measurements of diffusional anisotropy and RDCs and model-free analysis all show that the backbone of the hinge interdomain region of IFNAR2-EC is rigid on the picosecond to nanosecond time scale. Signal transduction in cytokines receptors is initiated by ligand-induced juxtaposition of the two receptor subunits, triggering the mutual phosphorylation of kinases associated to their cytoplasmic domains. The rigidity of the hinge ensures correct positioning of the receptor subunits in the ternary signaling complex and modulates the interaction between kinases in the cytoplasm, thereby controlling the rate and efficiency of phosphorylation.

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 Class II cytokine receptor (CRF2) family: overview and patterns of receptor–ligand interactions

Expanded genomic information has driven the discovery of new members of the human Class II family of cytokine receptors (CRF2), which now includes 12 proteins. The corresponding cytokines have been identified, paired with their receptors and initially characterized for function. These cytokines include: a new human Type I IFN, IFN-kappa; molecules related to IL-10 (IL-19, IL-20, IL-22, IL-24, IL-26); and IFN-lambdas (IL-28/29), which have antiviral and cell stimulatory activities reminiscent of Type I IFNs, but act through a distinct receptor. In response to ligand binding, the CRF2 proteins form heterodimers, leading to cytokine-specific cellular responses; these diverse physiological functions are just beginning to be explored. Progress in structural and mutational analysis of ligand-receptor interactions now presents a more reliable framework for understanding receptor-ligand interactions, and for predicting key regions in less well studied members of the CRF2 family. The relationships between the CRF2 proteins will be summarized, as will the progress in identifying patterns of receptor interactions with ligands.

Critical roles for IFN-beta in lymphoid development, myelopoiesis, and tumor development: links to tumor necrosis factor alpha

We have generated mice null for IFN-beta and report the diverse consequences of IFN-beta for both the innate and adaptive arms of immunity. Despite no abnormalities in the proportional balance of CD4 and CD8 T cell populations in the peripheral blood, thymus, and spleen of IFN-beta-/- mice, activated lymph node and splenic T lymphocytes exhibit enhanced T cell proliferation and decreased tumor necrosis factor alpha production, relative to IFN-beta+/+ mice. Notably, constitutive and induced expression of tumor necrosis factor alpha is reduced in the spleen and bone marrow (BM) macrophages, respectively, of IFN-beta-/- mice. We also observe an altered splenic architecture in IFN-beta-/- mice and a reduction in resident macrophages. We identify a potential defect in B cell maturation in IFN-beta-/- mice, associated with a decrease in B220+ve/high/CD43-ve BM-derived cells and a reduction in BP-1, IgM, and CD23 expression. Circulating IgM-, Mac-1-, and Gr-1-positive cells are also substantially decreased in IFN-beta-/- mice. The decrease in the numbers of circulating macrophages and granulocytes likely reflects defective maturation of primitive BM hematopoiesis in mice, shown by the reduction of colony-forming units, granulocyte-macrophage. We proceeded to evaluate the in vivo growth of malignant cells in the IFN-beta-/- background and give evidence that Lewis lung carcinoma-specific tumor growth is more aggressive in IFN-beta-/- mice. Taken altogether, our data suggest that, in addition to the direct growth-inhibitory effects on tumor cells, IFN-beta is required during different stages of maturation in the development of the immune system.