Characterization of human beta-interferon-binding sites on human cells

Induction of IFN-alphabeta enables Listeria monocytogenes to suppress macrophage activation by IFN-gamma

Production of type I interferon (IFN; IFN-alphabeta) increases host susceptibility to Listeria monocytogenes, whereas type II IFN (IFN-gamma) activates macrophages to resist infection. We show that these opposing immunological effects of IFN-alphabeta and IFN-gamma occur because of cross talk between the respective signaling pathways. We found that cultured macrophages infected with L. monocytogenes were refractory to IFN-gamma treatment as a result of down-regulation of the IFN-gamma receptor (IFNGR). The soluble factor responsible for these effects was identified as host IFN-alphabeta. Accordingly, macrophages and dendritic cells (DCs) showed reduced IFNGR1 expression and reduced responsiveness to IFN-gamma during systemic infection of IFN-alphabeta-responsive mice. Furthermore, the increased resistance of mice lacking the IFN-alphabeta receptor (IFNAR(-/-)) to L. monocytogenes correlated with increased expression of IFN-gamma-dependent activation markers by macrophages and DCs and was reversed by depletion of IFN-gamma. Thus, IFN-alphabeta produced in response to bacterial infection and other stimuli antagonizes the host response to IFN-gamma by down-regulating the IFNGR. Such cross talk permits prioritization of IFN-alphabeta-type immune responses and may contribute to the beneficial effects of IFN-beta in treatment of inflammatory diseases such as multiple sclerosis.

Interferons Alpha, Beta, and Omega

Interferon alpha (IFN-α) is a mixture of closely related proteins, termed “subtypes,” expressed from distinct chromosomal genes. Interferon β (IFN-β) is a single protein species and is molecularly related to IFN-α subtypes, although it is antigenically distinct from them. IFN omega (IFN-ω) is antigenically distinct from IFN-α and IFN-β but is molecularly related to both. The genes of three IFN subtypes are tandemly arranged on the short arm of chromosome 9. They are transiently expressed following induction by various exogenous stimuli, including viruses. They are synthesized from their respective mRNAs for relatively short periods following gene activation and are secreted to act, via specific cell surface receptors, on other cells. IFN-α subtypes are secreted proteins and as such are transcribed from mRNAs as precursor proteins, pre-IFN-α, containing N-terminal signal polypeptides of 23 hydrophobic amino acids (aa) mainly. Pre-IFN-β contains 187 aa, of which 21 comprise the N-terminal signal polypeptide and 166 comprise the mature IFN-β protein. IFN-ω contains 195 aa—the N-terminal 23 comprising the signal sequence and the remaining 172, the mature IFN-ω protein. At the C-terminus, the aa sequence of IFN-ω is six residues longer than that of IFN-α or IFN-β proteins. IFN-α, as a mixture of subtypes, and IFN-ω may be produced together following viral infection of null lymphocytes or monocytes/macrophages. The biological activities of IFNs are mostly dependent upon protein synthesis with selective subsets of proteins mediating individual activities. IFNs can also stimulate indirect antiviral and antitumor mechanisms, depending upon cellular differentiation and the induction of cytotoxic activity.

Identification of an adenine-nucleotide-binding site on interferon alpha2

Using 32P-labeled 2-azidoadenosine 5'-triphosphate (2N3ATP) and 8-azidoadenosine 5'-triphosphate (8N3ATP), we have identified a site on human interferon alpha2 (IFN-alpha2) that binds adenine nucleotides. The results from saturation and competition experiments demonstrated the specificity of the nucleotide interaction. Half-maximal saturation of IFN-alpha2 was observed at 10 microM 2N3ATP or 35 microM 8N3ATP. ATP effectively decreased photoinsertion of both photoaffinity analogs of ATP. Photoinsertion of 8N3ATP was enhanced by MgCl2, independent of the ionic strength, and exhibited an optimum pH between 7.0 and 7.5. Immobilized-Al3+ affinity chromatography and HPLC were used to purify the modified peptides from IFN-alpha2 that had been photolabeled with 8N3ATP and digested with trypsin or chymotrypsin. Overlapping-sequence analysis localized the sites of photoinsertion to the region corresponding to Lys121-Tyr135 in the amino acid sequence of IFN-alpha2, which almost perfectly overlaps a nuclear-localization signal (R120KYFQRITLYLKEKKY135).

Pharmacokinetics and antiviral activity of recombinant human interferon-beta ser17 in African green monkeys

The pharmacokinetics and antiviral activity of recombinant human interferon-beta ser17 (Betaseron) were evaluated in African green monkeys. In one study, animals infected with simian varicella virus were administered Betaseron intravenously (i.v.), intramuscularly (i.m.), or subcutaneously (s.c.) at doses of 1 x 10(6) or 1 x 10(7) IU/kg twice daily for 10 days. In another study, infected animals received Betaseron s.c. at doses of 1 x 10(6) IU/kg twice daily, 2 x 10(6) IU/kg once daily, 4 x 10(6) IU/kg every other day, or 6 x 10(6) IU/kg every 3 days for 10 days. Following i.v. administration, mean clearance, steady-state volume of distribution, and terminal half-life values for Betaseron were 0.36 +/- 0.08 liters/hr.kg, 0.65 +/- 0.09 liters/kg, and 1.9 +/- 0.43 h, respectively. Although bioavailability following i.m. and s.c. administration was only 30-50%, antiviral activity, as measured by reduction in viremia and appearance of skin rash, was comparable for i.v., i.m., and s.c. administration of 1 x 10(6) IU/kg of Betaseron twice daily. With increasing dose (1 x 10(6) IU/kg to 1 x 10(7) IU/kg), both the area under the serum concentration-time curve (AUC) and antiviral activity of Betaseron tended to increase. When comparing various s.c. dosing regimens, there was significant accumulation of Betaseron in serum with repeated twice-daily dosing. However, no accumulation of Betaseron in serum was observed if the dosing interval was less frequent than once daily. Antiviral activity was greatest with twice-daily or once-daily s.c. administrations of Betaseron.

Flow cytometric analysis of antineoplastic effects of interferon-alpha, beta and gamma labelled with fluorescein isothiocyanate on cultured brain tumors

Antineoplastic effects of interferons (IFNs) on brain tumors have often been reported in the literature, however, so far as we know, there are no reports of the study on the antineoplastic effect of IFNs (alpha, beta, and gamma) labelled with fluorescein isothiocyanate (FITC) using flow cytometry (FCM). Three established glioma cell lines and 11 cultured cells of brain tumor from surgical specimens were exposed to IFN-alpha, beta, and gamma at the concentrations of 10(2)-10(5) IU/ml for 24 h, respectively. Using FCM, the viability of the cells was evaluated with fluorescein diacetate stain and the cell cycle was analyzed from the DNA-histogram with propidium iodide stain. Furthermore, FITC-labelled IFN-alpha, beta and gamma were also contacted with each cell to calculate respective positive cells. The viability decreased about 60% on day 1 and day 3, indicating the effect of IFN-alpha and beta on U373MG cells and on some cultured glioma cells from surgical materials, whereas, IFN-gamma had no effects. Antineoplastic effect of each IFN well correlated with FITC-positive rates, demonstrating S phase block in the cell cycle. IFN-gamma had no antineoplastic effects, whereas IFN-alpha and beta showed antineoplastic effects, which fact suggested that IFN-gamma receptor be different from those of IFN-alpha and beta. The method of FITC-labelling for IFNs with the aid of FCM has the advantages as follows: 1) Antineoplasticity of IFN can be simply evaluated with FCM; 2) It is easy to analyze the action mechanism of IFN; 3) Information on the receptor is obtainable; and 4) Sensitivity can be evaluated prior to administration of IFN, suggesting possibilities of clinical application of this method.

Structure of the human interferon alpha receptor

The structure of the IFN alpha receptor has been studied by methods such as affinity crosslinking and gel chromatography over the last 8 years. The recent development of monoclonal antibodies against the receptor, and the cloning of an IFN alpha receptor cDNA has provided new important tools to understand the IFN alpha receptor structure. Thus, it has become obvious that the IFN alpha receptor has a more complex structure than first anticipated, probably involving more than one subunit. This review analyzes the present knowledge about the structure of the IFN alpha receptor, as well as many unresolved issues concerning this topic.

Stability of human interferon-beta 1: oligomeric human interferon-beta 1 is inactive but is reactivated by monomerization

Human interferon-beta 1 is extremely stable is a low ionic strength solution of pH 2 such as 10 mM HCl at 37 degrees C. However, the presence of 0.15 M NaCl led to a remarkable loss of antiviral activity. The molecular-sieve high-performance liquid chromatography revealed that, whereas completely active human interferon-beta 1 eluted as a 25 kDa species (monomeric form), the inactivated preparation eluted primarily as a 90 kDa species (oligomeric form). The specific activity (units per mg protein) of the oligomeric form was approx. 10% of that of the monomeric form. This observation shows that oligomeric human interferon-beta 1 is apparently in an inactive form. When the oligomeric eluate was resolved by polyacrylamide gel containing sodium dodecyl sulphate (SDS), it appeared to be monomeric under non-reducing conditions. Monomerization of the oligomeric human interferon-beta 1 by treatment with 1% SDS, fully regenerated its antiviral activity. These results suggest that the inactivation of the human interferon-beta 1 preparation was caused by its oligomerization via hydrophobic interactions without the formation of intermolecular disulphide bonds. These oligomers can be dissociated by SDS to restore biological activity.

A monoclonal antibody against the ligand binding site of the receptor for mouse interferon-gamma

A rat monoclonal IgG2a antibody, GR-20, has been produced against the receptor for mouse interferon-gamma (MuIFN-gamma). Comparison of competitive binding studies performed with either 125I-labeled GR-20 or recombinant (r) MuIFN-gamma, as well as a variety of other studies, suggested that the epitope recognized by the monoclonal antibody (mAb) is in the domain of the receptor that binds ligand. The binding of GR-20 to cells of the monomyelocytic line WEHI-3 was of high affinity (1-2 nM). Approximately 20,000 binding sites were found per cell, a value that is in close agreement with the number of MuIFN-gamma receptors quantified on cells of the same type by ligand binding studies. The mAb also bound to a variety of other mouse cells, suggesting that the same epitope is shared by receptors for MuIFN-gamma, regardless of cell type. The epitope was not detected on two human cell types that were tested, while cells of a rat cell line shown to be minimally responsive to rMuIFN-gamma gave equivocal binding results when they were interacted with GR-20. Binding of the mAb to the receptor did not mimic the effects of ligand. In fact, the opposite was true: binding blocked the induction of three biological effects of MuIFN-gamma, including priming of macrophages for tumor cell killing, upregulation of the expression of class II major histocompatibility antigens (Ia) on the same cell type, and induction of antiviral activity in L cells. Following intravenous injection, initial removal of GR-20 was precipitous, followed after 1 h by a phase which was more gradual, resulting in 5-10% of biologically active mAb remaining in the circulation after 24 h. Such retention should make this mAb useful in a variety of studies in vivo.

The cellular receptor of the alpha-beta interferons

This is a selective review of recent trends in research on the cellular receptor for the alpha-beta interferons. It deals mainly with work published in the last three years (1985-88), and therefore mainly with receptors for the human interferons. The binding characteristics of several human alpha interferons are examined, and the importance of in vitro experimental models for establishing the relationship between receptor binding and the cellular response is emphasized.

Immune interferon receptor: chemical and enzymatic sensitivity

Human immune interferon-gamma (HuIFN-gamma) labeled with 32P was used to study the structure of IFN-gamma receptor. When [32P]HuIFN-gamma was bound and crosslinked to IFN-gamma the receptor of human cells with a bifunctional crosslinker disuccinimidyl suberate (DSS), a single diffused 32P-labeled band corresponding to the IFN-gamma.receptor complex was visualized by SDS-polyacrylamide gel electrophoresis and autoradiography. The size of the [32P]-HuIFN-gamma.receptor complex was about 100-120 kD. Separation of crosslinked complex in reducing and nonreducing gels showed no size differences, suggesting the absence of interchain disulfide linkage. However, binding and formation of the crosslinked IFN-gamma. receptor complex on cells was diminished in the presence of the disulfide reducing agent dithiothreitol (DTT). The reduction was DTT-dose-dependent, suggesting that intramolecular disulfides of the receptor are important for binding. Also, [32P]HuIFN-gamma did not bind if cells were pretreated with and then washed free of DTT, suggesting an irreversible reduction of intrachain disulfide bonds, presumably of the receptor. [32P]HuIFN-gamma also specifically binds to human placental membranes. Each placenta has about 170 ng of IFN-gamma receptors. Covalent attachment of [32P]HuIFN-gamma to placental plasma membranes via DSS produced 2 crosslinked complexes with the molecular sizes of 100-120 kD and 60-70 kD. The IFN-gamma.receptor complex of placental membranes was solubilized with NP-40 after DSS treatment and partially purified with immobilized antibody to the carboxyl terminus of IFN-gamma. Treatment of the receptor complex with trypsin and papain was used to demonstrate its differential proteolytic sensitivity.

Structural characterization of fibroblast human interferon-beta 1

The complete amino acid sequence of fibroblast human interferon-beta 1 (IFN-beta 1) was determined, and the higher-order structure of the protein was characterized with Raman spectroscopy. That amino acid sequence was identical to the entire sequence deduced from the cDNA nucleotide sequence, showing there are no proteolytic cleavages of carboxy-terminal residues in contrast to natural human IFN-alpha and natural human IFN-gamma. The N-glycosylation site was confirmed as Asn-80 by the detection of glucosamines in the peptide containing Asn-80. An S-carboxymethyl Cys-17 was detected in the S-carboxymethylated protein, suggesting that Cys-17 is unpaired. Raman spectra indicated a predominance of alpha-helical backbone and three Cys residues in this protein form, one unpaired Cys residue and one disulfide bond. These results provide some evidence for the primary and higher-order structures of natural IFN-beta 1 so far predicted.

Preparation and characterization of biotinylated probes for the beta-interferon receptor

1. Recently we described the isolation of the beta-interferon receptor [Zhang et al. (1986) J. biol. Chem. 261, 8017-8021]. A highly purified product was obtained but in low quantities. 2. The use of biotinylated beta-interferon as a ligand represents an alternate approach to receptor isolation. 3. We have prepared and characterized the derivatives N-(biotinyl)- and N-(biotinyl-epsilon-aminocaproyl)-recombinant human [Ser17]-interferon beta (B- and BC-recHuIFN beta). 4. Biotin incorporation does not result in any loss of antiviral activity, demonstrating the recognition of the derivative by the cell receptor. 5. The biotinylated recHuIFN beta binds specifically and reversibly to succinoylavidin or guanidine thiocyanate-stripped succinoylavidin linked to a Sepharose matrix. 6. Comparison of the competition curves obtained with [14C]biotin and [3H]biotinyl recHuIFN, in the presence of increasing concentrations of biotin suggests that the IFN moiety of the derivative has little effect on the affinity of biotin for avidin. 7. Biotinylated recHuIFN beta derivatives represent useful probes for the beta-IFN receptor.

Reversion of the transformed phenotype of B16 mouse melanoma: involvement of an 83 kd cell surface glycoprotein in specific growth inhibition

Treating B16 mouse melanoma cells with monoclonal antibody NORM-2 reduces cell growth in tissue culture, agar, and syngeneic mice. We show that the NORM-2 antibody recognizes an integral 83 kd glycoprotein that is mobile in the plane of the plasma membrane of B16 melanoma cells. Expression of the glycoprotein is reduced under conditions that inhibit B16 growth, such as low serum, high cell density, and addition of transforming growth factor-beta. The glycoprotein reappears during S phase, when growth-arrested cells are restimulated. The NORM-2 antigen appears to be involved in growth regulation of B16 melanoma cells both in vitro and in vivo.

The interferon receptors

Early studies on the mode of action of interferons have indicated that a receptor system on the cell surface is involved in its action. The first direct evidence to a high-affinity binding site was found only after pure interferon was available. Two different receptors, one specific for interferons-alpha and beta, and the other for interferon-gamma were recognized. A correlation between affinity to the receptor and specific activity was established. Cross-linked complexes of labeled interferons with their receptors were visualized on gel electrophoresis and even partially purified. Internalization of interferons after binding to the receptor was reported. The role of gangliosides as helpers of interferon binding was recently investigated. Fragments of interferons which still retained binding capacity were described and helped in elucidating the binding site on the interferon molecule.

Human beta:alpha but not gamma interferon binding site is a product of the chromosome 21 interferon action gene

The binding of human interferons to their binding site(s) was measured by the amount of radioiodinated human beta interferon (HuIFNbeta) displaceable by unlabeled human beta, alpha, and gamma interferon (HuIFNbeta, alpha, and gamma). By this approach, HuIFNbeta and HuIFNalpha were found to interact with specific binding sites in cell membranes derived from human cells and mouse-human cell hybrids containing chromosome 21 as their only human chromosome. Specific binding was not observed with cell membranes derived from parental mouse cells or from mouse-human cell hybrids in subsequent generations that have lost human chromosome 21. Although the chromosome 21-positive mouse-human cell hybrids are sensitive to the antiviral effects of HuIFNbeta and HuIFNalpha, they are found to be insensitive to the antiviral effect of HuIFNgamma and to lack specific HuIFNgamma binding sites. These results suggest that the HuIFNbeta and HuIFNalpha but not HuIFNgamma binding sites are coded for by genes located on chromosome 21. The lack of a chromosome 21 gene dosage effect on the inducibility of the antiviral state by HuIFNgamma is consistent with this hypothesis.