Two IFNGR1 homologues in Tetraodon nigroviridis: Origin, expression analysis and ligand-binding preference.

In the present study, the divergent properties of IFNGR1 isoforms (IFNGR1-1 and IFNGR1-2) were characterized in Tetraodon nigroviridis. Despite the structural similarities between these proteins, two T. nigroviridis IFNGR1 homologues differ from each other not only in their primary nucleotide and amino acid sequences but also in their syntenic structure. Genomic analysis demonstrates the conservation of synteny between the fish IFNGR1-2s and IFNGR1s in higher vertebrates; conversely, the IFNGR1-1 has no corresponding conservation of synteny with Gallus gallus and Homo sapiens, suggesting that the two genes were derived from two different origins. Additionally, their different sensitivities to mitogens and recombinant T. nigroviridis IFN-γs were observed. Furthermore, ligand-binding analysis strongly supported the model proposed in Danio rerio, which suggests that IFNGR1-1 is the major component of the IFN-γrel receptor complex; IFN-γ most likely binds to both IFNGR1-2 and IFNGR1-1. This study is a further step towards elucidating the teleostean IFN-γ system, which is different from that in mammals.

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 human interferon alpha species and receptors.

Interferon (IFN) was approved by the U.S. Food and Drug Administration on June 5, 1986. As the first biotherapeutic approved, IFN-alpha paved the way for development of many other cytokines and growth factors. Nevertheless, we have just touched the surface of understanding the multitude of human IFNs. This paper reviews the history of the purification of human leukocyte IFN and key aspects of our current state of knowledge of human interferon alpha genes, proteins, and receptors.

Characterization of a soluble ternary complex formed between human interferon-beta-1a and its receptor chains.

The extracellular portions of the chains that comprise the human type I interferon receptor, IFNAR1 and IFNAR2, have been expressed and purified as recombinant soluble His-tagged proteins, and their interactions with each other and with human interferon-beta-1a (IFN-beta-1a) were studied by gel filtration and by cross-linking. By gel filtration, no stable binary complexes between IFN-beta-1a and IFNAR1, or between IFNAR1 and IFNAR2 were detected. However, a stable binary complex formed between IFN-beta-1a and IFNAR2. Analysis of binary complex formation using various molar excesses of IFN-beta-1a and IFNAR2 indicated that the complex had a 1:1 stoichiometry, and reducing SDS-PAGE of the binary complex treated with the cross-linking reagent dissucinimidyl glutarate (DSG) indicated that the major cross-linked species had an apparent Mr consistent with the sum of its two individual components. Gel filtration of a mixture of IFNAR1 and the IFN-beta-1a/IFNAR2 complex indicated that the three proteins formed a stable ternary complex. Analysis of ternary complex formation using various molar excesses of IFNAR1 and the IFN-beta-1a/IFNAR2 complex indicated that the ternary complex had a 1:1:1 stoichiometry, and reducing SDS-PAGE of the ternary complex treated with DSG indicated that the major cross-linked species had an apparent Mr consistent with the sum of its three individual components. We conclude that the ternary complex forms by the sequential association of IFN-beta-1a with IFNAR2, followed by the association of IFNAR1 with the preformed binary complex. The ability to produce the IFN-beta-1a/IFNAR2 and IFN-beta-1a/IFNAR1/IFNAR2 complexes make them attractive candidates for X-ray crystallography studies aimed at determining the molecular interactions between IFN-beta-1a and its receptor.

The purified myxoma virus gamma interferon receptor homolog M-T7 interacts with the heparin-binding domains of chemokines.

The myxoma virus T7 protein M-T7 is a functional soluble gamma interferon receptor homolog that has previously been shown to bind gamma interferon and inhibit its antiviral activities in a species-specific manner, but gene knockout analysis has suggested a further role for M-T7 in blocking leukocyte influx into infected lesions. We purified M-T7 to apparent homogeneity and showed that M-T7 is an N-linked glycoprotein that appears to be a stable homotrimer with a molecular mass of approximately 113 kDa in solution. M-T7, in addition to forming inhibitory complexes with rabbit gamma interferon, was also shown to bind to human interleukin-8, a prototypic member of the chemokine superfamily. Moreover, M-T7 was able to interact promiscuously with all members of the CXC, CC, and C chemokine subfamilies tested. Binding of human RANTES to M-T7 can be competed by rabbit gamma interferon and also by cold RANTES competitor with a 50% inhibitory concentration of 900 nM. Although M-T7 retains binding to a number of interleukin-8 N-terminal (ELR) deletion mutants, binding to mutants containing deletions in the C-terminal heparin-binding domain of interleukin-8 is abrogated. Furthermore, heparin effectively competes the interaction of M-T7 with the chemokine RANTES but not with rabbit gamma interferon. We propose that this novel M-T7 interaction with members of the chemokine superfamily may be facilitated through the conserved heparin-binding domains found in a wide spectrum of chemokines and that M-T7 may function by modulating chemokine-glycosaminoglycan interactions in virus-infected tissues.

Isolation of a biologically active soluble human interferon-alpha receptor-GST fusion protein expressed in Escherichia coli.

The cDNA encoding the extracellular domain of the human interferon-alpha (IFN-alpha) receptor (Uzé, G., Lutfalla, G., and Gresser, I. Cell 1990;60:225-234) lacking the signal peptide has been expressed in Escherichia coli as a fusion protein with glutathione S-transferase. The fusion protein represented 12% of total bacterial proteins and was found exclusively within cytoplasmic inclusion bodies. Inclusion body material was completely solubilized by 8 M urea; 20% solubilization was achieved by cell lysis in the presence of 0.45% cholamidopropyl dimethylammoniol-propane sulfonate and 1% Triton X-100. The soluble fusion protein was purified by gel filtration and affinity chromatography. Overall recovery of affinity purified fusion protein was approximately 100-200 micrograms/liter of cell culture. The affinity purified and refolded fusion protein exhibited the expected amino terminal sequence and M(r) of 68,000 on reduced sodium dodecylsulfate gel electrophoresis. The protein reacted with antibodies specific for the cloned IFN-alpha receptor and inhibited the antiviral and antiproliferative activities of recombinant IFN-alpha B. We have demonstrated that the fusion protein binds to IFN-alpha B and competes with the cell surface receptor for binding to this IFN-alpha species.

Possible involvement of Janus kinase Jak2 in interferon-gamma induction of nitric oxide synthase in rat glial cells.

To clarify the induction pathway of inducible nitric oxide (NO) synthase in the brain, we examined the effects of interferon-gamma and lipopolysaccharide on the induction of inducible NO synthase in glial cells cultured from neonatal rats, compared to those in the macrophage cell line RAW264.7 which was derived from Abelson leukemia virus-induced BALB/c lymphocytic lymphoma. NO synthase activity (NO2- accumulation) and 130 kDa protein of inducible NO synthase were induced 24 h after treatment with interferon-gamma or lipopolysaccharide in both glial cells and RAW264.7 macrophages. These induction activities were inhibited by a tyrosine kinase inhibitor, herbimycin A. Immunoprecipitation assay using antibodies against Janus kinases, and the signal transducer and activator of transcription-1 (STAT1), revealed that interferon-gamma induced tyrosine phosphorylation of the just another kinase-2 (Jak2) and STAT1 alpha but did not induced the phosphorylation of Jak1, the non-receptor tyrosine kinase-2 (Tyk2) and STAT1 beta. Tyrosine phosphorylation of Jak2 and STAT1 alpha induced by interferon-gamma was also inhibited by herbimycin A, while lipopolysaccharide did not induce any tyrosine phosphorylation of Janus kinases and STAT1 at all. These results suggest that the interferon-gamma-induced inducible NO synthase induction involves activation of Jak2-STAT1 alpha pathway in both glial cells and macrophages.

Comparative studies of gamma-interferon receptor-like proteins of variola major and variola minor viruses.

To study specific properties of the human gamma-interferon (gamma-IFN) receptor-like proteins of the highly virulent and low virulent strains of variola (smallpox) virus (VAR) recombinant plasmids determining synthesis of these proteins in E. coli cells have been constructed. The recombinant viral gamma-IFN receptor-like proteins have been found to have high interferon-neutralising activity with regard to human gamma-IFN but not murine gamma-IFN and human alpha-IFN. The variola major and variola minor proteins under study do not differ in the efficiency of human gamma-IFN antiviral activity inhibition.

Apparent heterogeneity of recombinant interferon gamma receptors produced in prokaryotic and eukaryotic expression systems.

Recombinant proteins show several types of heterogeneity and post-translational modifications which are usually related to their production system. The apparent heterogeneity of recombinant interferon gamma receptors and interferon gamma receptor-immunoglobulin G fusion proteins expressed in Escherichia coli, baculovirus-infected insect cells and Chinese hamster ovary cells have been studied. In general, all proteins tested showed some type of heterogeneity which was detectable by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The E. coli-derived receptor included non-native conformations involving mis-paired or non-formed disulfides. This type of heterogeneity affected the biological activity of the protein. In addition, the prokaryotic protein had trapped phosphoric acid during downstream processing. The phosphoric acid entrapment did not affect ligand binding capacity. The eukaryotic proteins showed heterogeneity because of the unequal cleavage of the signal peptide and because of differences in glycosylation. The latter types of heterogeneity did not affect activity. Glycosylation-related heterogeneity was partially derived from the unequal utilization of the potential N-glycosylation sites and differently affected the apparent molecular masses and migrations of the proteins on polyacrylamide gels. The results may be useful in characterization studies of recombinant proteins.

Crystallization of the complex of human IFN-gamma and the extracellular domain of the IFN-gamma receptor.

A complex of human interferon-gamma (IFN-gamma) with the soluble extracellular domain of the IFN-gamma receptor alpha-chain (IFN-gamma-R) has been crystallised. Crystals of the complex were grown using PEG 4000 as the precipitating agent in the presence of beta-octyl glucoside. The receptor-ligand complex crystallizes in a monoclinic space group and diffracts to about 3.0 A resolution. Isomorphous crystals have been obtained with complex containing selenomethionine and cysteine mutants of IFN-gamma, which may facilitate the ongoing X-ray structure determination.

Cloning and expression of a long form of the beta subunit of the interferon alpha beta receptor that is required for signaling.

The interferon alpha beta receptor (IFN alpha R) or type I IFN-R is formed by a 110-kDa alpha subunit or IFNAR and by a beta subunit, which has short and long forms (molecular masses of 55 and 95-100 kDa, respectively). In this report, we demonstrate that the IFN alpha/beta R cDNA recently cloned corresponds to the 55-kDa or short form of the beta subunit, while the 95-100-kDa species reported here corresponds to a longer form of the IFN alpha/beta R cDNA that is probably produced by alternative splicing of the same gene. Stable transfection of the alpha subunit with either form of the beta subunit results in the expression of low and high affinity receptors, while expression of either form of the beta subunit alone only produces low affinity receptors. More important, only expression of the alpha and long form of the human beta subunits in mouse L-929 cells reconstitutes the activation of the Jak kinases and the Stat factors, as well as the antiviral response to human type I IFNs.

Identification of functional type I and type II interferon receptors.

Although the interferons were the first cytokines purified and cloned, their receptors have remained an enigma as fully functional receptors have not been defined and characterized. We previously discovered that the IFN-gamma receptor (IFN-gamma R) was able to bind IFN-gamma, but required one or more accessory factors to exhibit functional activity. We have now identified a gene and sequence of one of these accessory factors. Both genomic and cDNA clones were used to reconstitute a functional receptor. The presence of the Hu-IFN-gamma R and the human accessory factor-1 (designated AF-1) are both necessary and sufficient to induce MHC class I antigens in response to Hu-IFN-gamma in hamster cells. AF-1 is a transmembrane protein with no significant amino acid homology to other sequences in nucleic acid data bases, but has overall structural homology to the class 2 cytokine receptor family. Whereas total human DNA was used to first isolate a Type I interferon receptor, the only genomic or cDNA clone reported exhibited activity essentially only in response to Hu-IFN-alpha B2 (Hu-IFN-alpha 8). Yet hamster or mouse cells containing human Chromosome 21 seemed to have the full complement of Hu-IFN-alpha activities and responded to all Hu-IFN-alpha species as well as Hu-IFN-beta. To investigate this dilemma, we extended our earlier studies with total human DNA to employ defined YAC clones. We have now isolated a genomic segment of human Chromosome 21 that exhibits the properties expected of the Type I interferon receptor: response to multiple species of Hu-IFN-alpha; and excellent binding of Hu-IFN-alpha A and Hu-IFN-alpha B2 species. Reconstitution of functional Type I and Type II interferon receptors now provides the first steps to link the receptors to the signal transduction mechanisms; and will help to integrate our understanding of the ligand receptor interactions to the molecular signals that activate specific transcription factors that in turn induce specific genes carrying the interferon regulatory elements.

Interferon-gamma induces tyrosine phosphorylation of interferon-gamma receptor and regulated association of protein tyrosine kinases, Jak1 and Jak2, with its receptor.

Interferon-gamma (IFN-gamma) induces the expression of a set of early response genes by tyrosine phosphorylation of latent transcription factors such as p91. Although the tyrosine kinases, Jak1 and Jak2, have recently been shown to be critical for signal transduction by IFN-gamma, evidence is lacking for both tyrosine phosphorylation of the IFN-gamma receptor (IFN-gamma R) and the interaction between Jak1, Jak2, and the IFN-gamma R. In this report, we show that binding of IFN-gamma to HeLa cells initiated a series of events that resulted in the extremely rapid (15 s) tyrosine phosphorylation of not only Jak1, Jak2, and p91 but also the IFN-gamma R. Coimmunoprecipitation experiments revealed that Jak1 was associated with the IFN-gamma R prior to ligand binding, whereas Jak2 became part of the IFN-gamma R-Jak1 complex immediately after ligand binding. H2O2/vanadate treatment of cells for 15 min resulted in only the tyrosine phosphorylation of Jak1 and IFN-gamma R. Only after 60 min of this treatment did we observe tyrosine phosphorylation of Jak2 and p91 and assembly of the transcription factor complex FcRF gamma that binds to the promoter of the fcgr1 gene. These data suggest that JAK1 associates with the IFN-gamma R prior to ligand binding. IFN-gamma treatment of cells results in recruitment of JAK2 into the IFN-gamma R-Jak1 complex followed by assembly of the transcription factor FcRF gamma complex.

The human interferon alpha/beta receptor: characterization and molecular cloning.

We describe a universal ligand-binding receptor for human interferons alpha and interferon beta (type I IFNs). A soluble 40 kDa IFN-alpha/beta receptor (p40) that blocks the activity of type I IFNs was purified from urine and sequenced. Antibodies raised against p40 completely block the activity of several type I IFNs and immuno-precipitate both a cellular 102 kDa IFN-alpha/beta receptor and its cross-linked complexes with IFN-alpha 2. The receptor is a disulfide-linked dimer, consisting of 51 kDa subunits. We isolated and expressed a 1.5 kb cDNA, coding for the IFN-alpha/beta receptor. Its 331 amino acid sequence includes a leader and a transmembrane region, while its ectodomain corresponds to p40. IFN-alpha/beta receptor is physically associated with the cytoplasmic Tyr kinase JAK1, hence, in addition to ligand binding, it is directly involved in signal transduction.

Expression of complete human IFN-gamma receptor and its extracellular domain in insect cells: purification and characterization of the recombinant proteins.

We here describe an efficient procedure for overexpression and purification of recombinant complete human interferon-gamma (IFN-gamma) receptor (IFN-gamma-R) and its extracellular fragment employing a baculovirus (BV) expression system. Infection of Sf 158 cells with recombinant BV results in membrane expression of high affinity IFN-gamma-R (Kd 1.6 x 10(-10) M), with approximately 10(6) molecules/cell 40 h postinfection. Solubilized, affinity-purified IFN-gamma-R and a secreted extracellular domain of IFN-gamma-R were compared for ligand-binding capacity and antagonistic activity in an IFN-gamma bioassay. Our results show that the complete receptor has a 2.5-fold higher ligand affinity and a 15-fold higher IFN-gamma in vitro-neutralizing capacity in an in vitro virus protection assay as compared to the extracellular fragment. This suggests that the transmembrane and cytoplasmic domains of IFN-gamma-R contribute to stability and/or enhance formation of biologically active receptor complexes in solution.

Interferon-gamma induces receptor dimerization in solution and on cells.

The extracellular domain (ECD) of the human interferon-gamma (IFN gamma) receptor was stably expressed in Chinese hamster ovary cells and purified to homogeneity. Scatchard analysis of 125I-IFN gamma binding to ECD preparations revealed the formation of a ligand-receptor complex which displayed a Ka of 6.4 +/- 0.9 x 10(8) M-1. Two types of complexes were identified by sucrose density gradient ultracentrifugation. The stoichiometry of the major ECD-ligand complex was determined by high performance liquid chromatography gel filtration. When IFN gamma was incubated with a 2-fold molar excess of ECD, a 190-kDa complex was isolated that contained 2 mol of ECD per 1 mol of IFN gamma. IFN gamma also induced dimerization of IFN gamma receptors expressed at the cell surface as detected by chemically cross-linking receptor bound ligand and analyzing cell lysates by SDS-polyacrylamide gel electrophoresis and immunoblotting. Finally, labeled forms of ECD bound to cells preincubated at 4 degrees C with excess amounts of IFN gamma indicating that the ligand could associate with more than one receptor molecule in the absence of chemical cross-linking agents. These results demonstrate that IFN gamma effects dimerization of its receptor under physiologic conditions and suggest that IFN gamma receptor dimerization may be an important event in inducing IFN gamma-dependent biologic responses.

Purification of interferon gamma-interferon gamma receptor complexes by preparative electrophoresis on native gels.

Cytokine-receptor complexes are required for certain studies including crystallization, NMR spectra, and investigation of the biological response mechanism to the cytokine. The purity of the ligand-receptor complex is critical for most of these applications. We investigated the possibility of purifying protein-protein complexes by electrophoresis on native gels. Starting with partially purified mouse and highly purified human proteins, we prepared milligram amounts of interferon gamma-interferon gamma receptor complexes by preparative electrophoresis on nondenaturing polyacrylamide gels. In both cases, pure ligand-receptor complexes with the correct stoichiometry of binding were recovered. Electrophoresis on preparative native gels may prove to be of general interest for the preparation of protein-protein complexes to be used in diverse studies.

Interferon alpha induces rapid tyrosine phosphorylation of the alpha subunit of its receptor.

The mechanisms of generation of second messengers after binding of interferon alpha (IFN alpha) to its receptor remain unknown. We have studied the phosphorylation of the alpha subunit of the IFN alpha receptor, which is recognized by the monoclonal antibody IFNa receptor 3. Immunoblotting experiments showed that IFN alpha induced rapid tyrosine phosphorylation of the alpha subunit in the IFN alpha-sensitive H-929, U-266, and Daudi cell lines. Immunoprecipitation experiments performed with 32P-labeled cells showed that the alpha subunit is phosphorylated before IFN alpha treatment and that the level of phosphorylation increases after IFN alpha stimulation. Phosphoamino acid analysis confirmed the IFN alpha-induced tyrosine phosphorylation and demonstrated that the base-line phosphorylation corresponded to serine phosphorylation that increased 50% upon IFN alpha treatment. Tyrosine phosphorylation of the alpha subunit was time- and dose-dependent, further demonstrating the specificity of the process. Phosphorylation of the alpha subunit of the receptor occurred rapidly after IFN alpha binding, both at 37 and 4 degrees C. Exposure of the cells to the tyrosine kinase inhibitor genistein blocked the IFN alpha-induced tyrosine phosphorylation of this subunit of the IFN alpha receptor. In contrast H7, a specific protein kinase C inhibitor, and acute and chronic exposure to phorbol esters had no effect on tyrosine phosphorylation, suggesting that protein kinase C does not regulate the tyrosine phosphorylation of the alpha subunit of the IFN alpha receptor. No IFN alpha-induced tyrosine phosphorylation was observed in the IFN alpha-resistant U-937 cell line that expresses a variant IFN alpha receptor. Altogether these data suggest that tyrosine phosphorylation of the alpha subunit may play a role in the signal transduction pathway of IFN alpha.