Characterization of three monoclonal antibodies that recognize the interferon alpha 2 receptor

Type I interferon therapies of multiple sclerosis and hepatitis C virus infection

Interferons type I (IFN-I), activated following a bacterial or viral infection, play a major role in the induction and regulation of the immune system. The immune response results in viral RNA and binds to receptors such as RIG-I-like receptors (RLRs) or Toll-like receptors, leading to the IFN-I signaling cascade. Thanks to its cellular function, IFN-I is widely used in therapies for such diseases as multiple sclerosis (MS) and hepatitis C disease (HCD).

MS is a neurological, autoimmune, chronic inflammatory disease of the central nervous system (CNS). During MS, nerve cell demyelination is observed due to the myelin heaths and oligodendrocyte damage. As a result, neuronal signal and neuron communication are attenuated. The mechanism of MS is still unknown. MS therapy applies interferon-β (IFN-β). IFN-β therapy has been used since the last century, but the therapeutic mechanism of IFN-β has not been completely understood. MS can lead to four syndromes: clinically isolated syndrome (CIS), relapsing-remitting MS (RRMS), primary progressive MS (PPMS), and secondary progressive MS (SPMS).

HCD occurs as a result of infection with the hepatitis C virus (HCV), belonging to the Flaviviridae family. HCV is a blood-borne virus with a positive single-stranded RNA. A vaccine for HCV is not available yet. HCD can lead to liver damage or cancer. In HCD interferon-α therapy (IFN-α) is applied. As with MS, the mechanism of IFN-α therapy is not completely known.

Molecular cloning and sequencing analysis of the interferon receptor (IFNAR-1) from Columba livia

OBJECTIVE

Partial sequence cloning of interferon receptor (IFNAR-1) of Columba livia.

MATERIAL AND METHODS

In order to obtain a certain length (630 bp) of gene, a pair of primers was designed according to the conserved nucleotide sequence of Gallus (EU477527.1) and Taeniopygia guttata (XM_002189232.1) IFNAR-1 gene fragment that was published by GenBank. Special primers were designed by the Race method to amplify the 3'terminal cDNA.

RESULTS

The Columba livia IFNAR-1 displayed 88.5%, 80.5% and 73.8% nucleotide identity to Falco peregrinus, Gallus and Taeniopygia guttata, respectively. Phylogenetic analysis of the IFNAR1 gene showed that the relationship of Columba livia, Falco peregrinus and chicken had high homology.

CONCLUSIONS

We successfully obtained a Columba livia IFNAR-1 gene partial sequence. Analysis of the genetic tree showed that the relationship of Columba livia and Falco peregrinus IFNAR-1 had high homology. This result can be used as reference for further research and practical application.

Decreased type I interferon receptor-soluble isoform in antiretroviral-treated HIV-positive children

We developed a real-time PCR assay to simultaneously measure the mRNA level of type I interferon (IFN) receptor (IFNAR) components in peripheral blood cells of children with chronic immune stimulation due to HIV infection. All patients were undergoing antiretroviral therapy and were divided into two groups on the basis of the induction of MxA mRNA, a marker of type I IFN bioactivity. We found that IFNAR-2 subunit mRNA was higher than that of the IFNAR-1 subunit, that the mRNA for the IFNAR-2.2 functional isoform was more expressed than that for the truncated IFNAR-2.1 isoform, and both were much more represented than that of the IFNAR-2.3 soluble isoform. We also demonstrated that soluble isoform mRNA was significantly diminished in the subgroup of patients with MxA mRNA below the cutoff value (determined as the 99th percentile of MxA measured in healthy controls). These results suggest that downregulation of the soluble receptor isoform, which would not compete with the functional isoform for binding to the target cytokine, would give type I IFN, eventually induced in these patients in the case of viral reactivation, the opportunity to promptly exert its antiviral activity.

Interferon: The pathways of discovery

This historical account covers 50 years of seminal research work on interferon done since its discovery in 1957. Topics related to molecular structure, production and action of interferons are considered from the viewpoint of how our insights have expanded and deepened within the context of evolving tools and general knowledge in cellular and molecular biology. Lines of thought that linked each discovery to the next are expounded.

Temporal expression of type I interferon receptor in the peri-implantation ovine extra-embryonic membranes: demonstration that human IFNalpha can bind to this receptor

Interferon-tau (IFNtau), produced by the trophectoderm of ruminant ungulates, binds to the type I IFN receptor (IFNAR) located at the uterine endometrium in a paracrine manner. Since IFNtau attenuates the secretory pattern of an endometrial luteolysin, prostaglandin F2alpha, IFNtau has been considered as a conceptus factor implicated in the process of maternal recognition of pregnancy. Here we report the presence of IFNAR subunit (IFNAR1) in ovine conceptuses during the period of peri-implantation development and demonstrate that 125I-human (h) IFNalpha binds to membrane preparations from ovine corpus luteum and conceptus. Using an antibody against hIFNAR1, immunohistochemical analysis revealed that IFNAR1 protein was present in day 14 and 16 conceptuses (day 0 = day of estrus) and luminal and glandular epithelia of the endometrium. Conceptus membrane proteins analyzed by western blot with the same antibody displayed immunoreactive bands at 95, 60 and 55 kDa while endometrial membrane proteins showed bands at 200, 95 and 55 kDa. Northern blot analysis revealed that IFNAR1 mRNA was present in days 15-19 conceptuses and day 18-19 allantoic membranes. Receptor binding studies indicated that 125I-hIFNalpha binding to day 16, but not earlier, conceptus membrane proteins could be displaced with hIFNalpha or ovine IFNtau. Based on Scatchard analysis, day 16 conceptus membranes contained 28 fmol IFNAR/mg protein with a dissociation constant of 300 pM. Cross-linking experiments demonstrated that 125I-hIFNalpha-receptor complex migrated at 120 kDa, indicating that the receptor component(s) was approximately 100 kDa. These data provide evidence that although the binding does not occur until day 16, ovine conceptuses possess IFNAR1 near or at the time of implantation, suggesting that IFNtau, a factor produced by the trophectoderm of ruminant ungulates, could act on the conceptus in an autocrine manner. In addition to functioning as an antiluteolytic factor, therefore, IFNtau may have a direct effect on conceptus development.

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.

The proximal tyrosines of the cytoplasmic domain of the beta chain of the type I interferon receptor are essential for signal transducer and activator of transcription (Stat) 2 activation. Evidence that two Stat2 sites are required to reach a threshold of interferon alpha-induced Stat2 tyrosine phosphorylation that allows normal formation of interferon-stimulated gene factor 3

The precise role of the different subunits (alpha/IFNAR1 and betaL/IFNAR2) of the type I interferon receptor (IFN-R) in the activation of signal transducer and activator of transcription (Stat) 1, Stat2, and Stat3 has not yet been established. In this report we demonstrate that there are functionally redundant phosphotyrosine-dependent and -independent binding sites for Stat2 in the alpha and beta subunits of the type I IFN-R. Expression of a type I IFN-R containing only the constitutive Stat2 site or the proximal tyrosines of betaL, but not the docking site on the alpha chain (Tyr466 and Tyr481), supported low levels of Stat2 activation. However, the presence of only one intact Stat2 site did not lead to induction of interferon-stimulated gene factor 3 (ISGF3) or an antiviral state. Normal levels of Stat2 tyrosine phosphorylation, induction of ISGF3, and an antiviral effect always required the proximal tyrosines of betaL and at least one of the other Stat2 sites (Tyralpha466, 481 or betaL404-462). These data suggest that a threshold of Stat2 tyrosine phosphorylation is required for complete activation of ISGF3. Interestingly, a receptor in which all tyrosines were mutated to phenylalanine shows normal Stat3 phosphorylation and low levels of activation of Stat1.

Characterization of antihuman IFNAR-1 monoclonal antibodies: epitope localization and functional analysis

The type I interferon receptor (IFNAR) is composed of two subunits, IFNAR-1 and IFNAR-2, encoding transmembrane polypeptides. IFNAR-2 has a dominant role in ligand binding, but IFNAR-1 contributes to binding affinity and to differential ligand recognition. A panel of five monoclonal antibodies (mAb) to human IFNAR-1 (HuIFNAR-1) was produced and characterized. The reactivity of each mAb toward HuIFNAR-1 on native and transfected cells and in Western blot and ELISA formats was determined. In functional assays, one mAb, EA12, blocked IFN-a2 binding to human cells and interfered with Stat activation and antiviral activity. Epitopes for the mAb were localized to subdomains of the HuIFNAR-1 extracellular domain by differential reactivity of the mAb to a series of human/bovine IFNAR-1 chimeras. The antibody EA12 seems to require native HuIFNAR-1 for reactivity and does not map to a single subdomain, perhaps recognizing an epitope containing noncontiguous sequences in at least two subdomains. In contrast, the epitopes of the non-neutralizing mAb FB2, AA3, and GB8 mapped, respectively, to the first, second, and third subdomains of HuIFNAR-1. The mAb DB2 primarily maps to the fourth subdomain, although its reactivity may be affected by other determinants.

Identification of a domain in the beta subunit of the type I interferon (IFN) receptor that exhibits a negative regulatory effect in the growth inhibitory action of type I IFNs

Expression of human alpha and long form of the beta (betaL) subunits of type I interferon receptor (IFN-R) in mouse cells is sufficient to activate the Jak-Stat pathway and to elicit an antiviral state in response to human IFNalpha2 and IFNbeta. We demonstrate herein, however, that these cells respond to the antiproliferative effects of murine IFNalphabeta but not human type I IFNs. These results suggest that an unknown species-specific component is required for the antiproliferative effect of human type I IFNs. The absence of this component can be complemented by expressing the human betaL chain truncated at amino acid 346. Thus, the distal region of betaL appears to function as a negative regulator of the growth inhibitory effects of type I IFNs. Further studies looking for possible targets of the betaL regulatory domain demonstrated that this region associates with a tyrosine phosphatase. These results suggest that a protein associated with the negative regulatory domain of betaL, likely a tyrosine phosphatase, plays a role in regulating the growth inhibitory effects of human type I IFNs.

Differential use of the betaL subunit of the type I interferon (IFN) receptor determines signaling specificity for IFNalpha2 and IFNbeta

The signaling specificity for cytokines that have common receptor subunits is achieved by the presence of additional cytokine-specific receptor components. In the type I interferon (IFN) family, all 14 subtypes of IFNalpha, IFNbeta, and IFNomega bind to the same alpha and betaL subunits of the type I IFN-R, yet differences in signaling and biological effects exist among them. Our data demonstrate that IFNalpha2 and IFNbeta utilize different regions of the betaL subunit for signaling. Thus, in contrast to other cytokine systems, signal diversity in the type I IFN system can be accomplished within the same receptor complex by utilizing different regions of the same receptor subunits.

A region of the beta subunit of the interferon alpha receptor different from box 1 interacts with Jak1 and is sufficient to activate the Jak-Stat pathway and induce an antiviral state

Coexpression of the alpha and betaL subunits of the human interferon alpha (IFNalpha) receptor is required for the induction of an antiviral state by human IFNalpha. To explore the role of the different domains of the betaL subunit in IFNalpha signaling, we coexpressed wild-type alpha subunit and truncated forms of the betaL chain in L-929 cells. Our results demonstrated that the first 82 amino acids (AAs) (AAs 265-346) of the cytoplasmic domain of the betaL chain are sufficient to activate the Jak-Stat pathway and trigger an antiviral state after IFNalpha2 binding to the receptor. This region of the betaL chain, required for Jak1 binding and activation, contains the Box 1 motif that is important for the interaction of some cytokine receptors with Jak kinases. However, using glutathione S-transferase fusion proteins containing amino- and carboxyl-terminal deletions of the betaL cytoplasmic domain, we demonstrate that the main Jak1-binding region (corresponding to AAs 300-346 on the beta subunit) is distinct from the Box 1 domain (AAs 287-295).

Distribution of type-I interferon-receptors in human first trimester and term placental tissues and on isolated trophoblast cells

PROBLEM

Type-I interferon (IFN) is the protein recognizing pregnancy in ruminants. Although IFN is secreted in early pregnancy, its role is not still clear in other species. Like other cytokines, IFN exerts its biological functions through specific membrane receptors. We have investigated the potential action of IFN in human pregnancy by studying the distribution of the receptors in the human placenta.

METHOD

Reactivity to monoclonal antibodies (mAbs) to the type-I IFN-receptor (R) was analyzed by immunohistochemistry in human placental tissues and in cytospins of first trimester trophoblast cells.

RESULTS

Type-I IFN-R immunoreactivity was observed mostly in first trimester villous cytotrophoblasts and in the cytotrophoblast cell columns. Trophoblast in the decidua, the epithelium of the uterine glands, and most of the isolated trophoblast cells were also immunoreactive.

CONCLUSION

The expression of type-I IFN-R in the highly proliferating and migrating trophoblast suggests that this cytokine has a role in trophoblast growth and invasion.

A protein-arginine methyltransferase binds to the intracytoplasmic domain of the IFNAR1 chain in the type I interferon receptor

The intracytoplasmic domain (IC) of cytokine receptors provides docking sites for proteins which mediate signal transduction. Thus, in interferon-alpha,beta receptors (IFNAR1 and 2), the IC region binds protein-tyrosine and -serine/threonine kinases which phosphorylate the receptor and the associated Stat transcription factors. A two-hybrid screening was carried out to identify additional proteins which could interact with the IC domain of the IFNAR1 chain of the IFN-alpha,beta receptor. Several positive clones representing a protein sequence designated IR1B4 were recovered from a human cDNA library. IR1B4 was identified as the human homolog of PRMT1, a protein-arginine methyltransferase from rat cells. Flag-IR1B4 fusion proteins bind to the isolated IFNAR1 intracytoplasmic domain produced in Escherichia coli, as well as to the intact IFNAR1 chain extracted by detergent from human U266 cell membranes. S-Adenosylmethionine-dependent methyltransferase activity was precipitated by anti-IFNAR1 antibodies from untreated human cells. IR1B4/PRMT1 is involved in IFN action since U266 cells rendered deficient in this methyltransferase by antisense oligonucleotides become more resistant to growth inhibition by IFN. Methylation of proteins by enzymes which can attach to the IC domains of receptors may be a signaling mechanism complementing protein phosphorylation. Among substrates methylated by PRMT1 are RNA-binding heterogeneous nuclear ribonucleoproteins (hnRNPs) which are involved in mRNA processing, splicing and transport into the cytoplasm.

Human interferon-alpha receptor: identification of the region involved in binding to interferon-alpha B

Three polypeptides comprising amino acids 1-102, 93-260, and 261-410 of the extracellular domain of the human interferon-alpha receptor HuIFN-alpha R (Uzé, G., Lutfalla, G., and Gresser, I. Cell 1990; 60:225-234) have been expressed in Escherichia coli. The polypeptides were sequestered within bacterial inclusion bodies. Inclusion body material was solubilized by 8 M urea, and the polypeptides were purified by gel filtration or histidine tag-based affinity chromatography. Overall recovery of each purified and refolded polypeptide was approximately 0.5-0.8 mg/liter of cell culture. The polypeptides migrated as homogeneous monomers of 12 kDa, 22 kDa, and 17 kDa, respectively on reduced sodium dodecylsulfate polyacrylamide gel electrophoresis. The polypeptide fragments corresponding to amino acids 1-102, and 93-260 of the extracellular domain of HuIFN-alpha R lacked the ability to bind to IFN-alpha B and to inhibit its biologic activities. The polypeptide fragment corresponding to amino acids 261-410 of the receptor molecule inhibited the antiproliferative activity of IFN-alpha B and competed with the Daudi cell surface receptor for binding to this IFN-alpha species.

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.

Expression and signaling specificity of the IFNAR chain of the type I interferon receptor complex

The IFNAR chain of the type I interferon (IFN) receptor (IFNIR) undergoes rapid ligand-dependent tyrosine phosphorylation and acts as a species-specific transducer for type I IFN action. Using the vaccinia/T7 expression system to amplify IFNAR expression, we found that human HeLa-S3 cells transiently express high levels of cell surface IFNAR chains (approximately 250,000 chains per cell). Metabolic labeling and immunoblot analysis of transfected HeLa cells show that the IFNAR chain is initially detected as 65-kDa and 98-kDa precursors, and then as the 130-kDa mature protein. Due to variation in N-glycosylation, the apparent molecular mass of the mature IFNAR chain varies from 105 to 135 kDa in different cells. IFNIR structure was characterized in various human cell lines by analyzing 125I-labeled IFN cross-linked complexes recognized by various antibodies against IFNIR subunits and JAK protein-tyrosine kinases. Precipitation of cross-linked material from Daudi cells with anti-IFNAR antibodies showed that IFNAR was present in a 240-kDa complex. Precipitation of cross-linked material from U937 cells with anti-TYK2 sera revealed a 240-kDa complex, which apparently did not contain IFNAR and was not present in IFN-resistant HEC1B cells. The tyrosine phosphorylation and down-regulation of the IFNAR chain were induced by type I IFN in several human cell lines of diverse origins but not in HEC1B cells. However, of type I IFNs, IFN-beta uniquely induced the tyrosine phosphorylation of a 105-kDa protein associated with the IFNAR chain in two lymphoblastoid cell lines (Daudi and U266), demonstrating the specificity of transmembrane signaling for IFN-beta and IFN-alpha through the IFNAR chain.

Interaction of the transcriptional activator Stat-2 with the type I interferon receptor

Binding of interferon-alpha (IFN alpha) to the multisubunit type I IFN receptor (IFNR) induces activation of the Tyk-2 and Jak-1 kinases and tyrosine phosphorylation of multiple signaling elements, including the Stat proteins that form the ISGF3 alpha complex. Although Jak kinases are required for IFN alpha-dependent activation of Stats, the mechanisms by which Stats interact with these kinases are not known. We report that Stat-2 associates with beta s subunit of the type I IFN receptor in an interferon-dependent manner. This association is rapid, occurring within 1 min of interferon treatment of cells, and is inducible by various type I (alpha, beta, omega) but not type II (gamma) IFNs. The kinetics of Stat-2-IFNR association are similar to the kinetics of phosphorylation of Stat-2, suggesting that during its binding to the type I IFNR, Stat 2 acts as a substrate for interferon-dependent tyrosine kinase activity. These findings support the hypothesis that the type I IFNR acts as an adaptor, linking Stat proteins to Jak kinases. Interaction of Stat-2 with the beta s subunit of the type I IFNR may be a critical signaling event, required for the formation of the ISGF3 alpha complex and downstream transcription of interferon-stimulated genes.

Configuration of the interferon-alpha/beta receptor complex determines the context of the biological response

Constituents of the Type 1 interferon (IFN) receptor (IFNABR) identified to date include the alpha and beta transmembrane subunits and the associated intracellular kinases, Jak 1 and Tyk 2. In this report, we demonstrate that a human cell type that expresses both subunits of IFNABR, together with Jak 1 and Tyk 2, exhibits a limited binding capacity for and is only partially sensitive to the effects of IFN-alpha/beta, despite adequate levels of the cytoplasmic transcription factors Stat1, Stat2, and Stat3. Specifically, a low affinity interaction between IFN-alpha/beta and cell surface receptors results in ISGF3 (Stat1:2) activation and an antiviral response, yet no IFN-inducible growth inhibition. Using a panel of murine cells that are variably configured with respect to the human IFNABR-alpha/beta subunits, we provide evidence that an additional component(s) encoded on human chromosome 21 is required to confer high affinity binding and IFN-inducible growth inhibition to cells that express the alpha and beta subunits of the IFNABR. The data indicate that transcriptional activation that leads to an antiviral response is mediated by IFN-alpha/beta activation of IFNABR-alpha and IFNABR-beta in the context of a low affinity interaction, yet a high affinity interaction is necessary for signal transducing events that mediate growth inhibition. We provide evidence that the extent of ISGF3 activation correlates directly with the magnitude of an antiviral but not a growth inhibitory response.

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.

Vaccinia virus B18R gene encodes a type I interferon-binding protein that blocks interferon alpha transmembrane signaling

Poxviruses encode a large number of proteins that attenuate the inflammatory and immune responses to infection. In this report we demonstrate that a number of orthopoxviruses express a type I interferon (IFN)-binding protein, which is encoded by the B18R open reading frame in the WR strain of vaccinia virus. The B18R protein has significant regions of homology with the alpha subunits of the mouse, human, and bovine type I IFN receptors, bound human IFN alpha 2 with high affinity, and inhibited transmembrane signaling as demonstrated by inhibition of Fc receptor factor gamma 1/gamma 2 and interferon-stimulated gene factor-3 formation as well as inhibition of the IFN alpha antiviral response. Among viral host response modifiers, the B18R protein is unique inasmuch as it exists as a soluble extracellular as well as a cell surface protein and thus should effectively block both autocrine and paracrine functions of IFN.

Transmembrane signaling by the alpha subunit of the type I interferon receptor is essential for activation of the JAK kinases and the transcriptional factor ISGF3

The Type I interferon (IFN) receptor has a multisubunit structure. The component of the receptor that has been most thoroughly studied is the alpha subunit. Expression of the alpha subunit in mouse L-929 cells confers antiviral response to human IFN alpha 8, but not to human IFN alpha 2 or IFN beta. This antiviral effect is observed without a significant increase in IFN binding. It has not been determined why mouse cells expressing the human alpha subunit show different response to the antiviral activity of distinct human Type I IFNs. In this report, we demonstrate that the response to human Type I IFNs in mouse cells expressing the alpha subunit is dependent on cross-binding to the mouse receptor. This is supported by the finding that human IFN alpha 8, but not human IFN alpha 2, cross-binds to the mouse receptor even in the absence of expression of the human alpha subunit. We also demonstrate that only mouse cells expressing the human alpha subunit are able to tyrosine-phosphorylate p135tyk2 and JAK-1 and to form the ISGF3 complex in response to human IFN alpha 8. These results demonstrate that the alpha subunit is essential for IFN alpha signaling through the JAK kinases and ISGF3.

Characterization of a domain of a human type I interferon receptor protein involved in ligand binding

Two monoclonal antibodies that recognize different epitopes of the extracellular domain of one of the proteins that constitute the type I interferon receptor were used to delineate the interferon binding site. Antibody 64G12 both inhibits the binding of radiolabeled interferon-alpha 2 and IFN-alpha 8 to their cell surface receptors and neutralizes the antiviral and antiproliferative actions of all the type I interferons tested, including IFN-beta, IFN-omega, and human leukocyte IFN, a mixture of different interferon-alpha isotypes. Antibody 34F10 recognizes the type I interferon receptor with an affinity similar to that of the MAb 64G12 but does not inhibit either the binding or the biologic activity of any of the type I interferons tested. Both antibodies recognize a protein of 105 +/- 5 kD from either Daudi or Ly28 cells. Immunoprecipitation following surface iodination demonstrated that the neutralizing MAb recognizes a protein of 105 kD and the nonneutralizing MAb a protein of 110 kD in extracts of Daudi cells. A second less intense band was also detected by both antibodies. Cross-linking of IFN-alpha 2 to its receptor before immunoprecipitation prevented the neutralizing antibody from immunoprecipitating the receptor protein, but the nonneutralizing MAb was still able to recognize a 140 kD protein corresponding to the cross-linked interferon-receptor protein complex. Thus, an interferon binding domain appears to be localized in a region between amino acids 23 and 229 of the extracellular domain of a transmembrane protein that forms part of the type I interferon receptor complex containing the epitopes recognized by each antibody.

Direct binding to and tyrosine phosphorylation of the alpha subunit of the type I interferon receptor by p135tyk2 tyrosine kinase

Binding of type I interferons (IFNs) to their receptors induces rapid tyrosine phosphorylation of multiple proteins, including the alpha and beta subunits of the receptor, the polypeptides that form the transcriptional activator ISGF3 alpha (Stat113, Stat84, and Stat91), and the p135tyk2 and Jak-1 tyrosine kinases. In this report, we demonstrate that the alpha subunit of the type I IFN receptor (IFN-R) corresponds to the product of a previously cloned receptor subunit cDNA and, further, that the p135tyk2 tyrosine kinase directly binds and tyrosine phosphorylates this receptor subunit. Glutathione S-transferase (GST) fusion proteins encoding the different regions of the cytoplasmic domain of the alpha subunit can bind the p135tyk2 contained in human cell lysates. The association between the alpha subunit and Tyk2 was demonstrated by immunoblotting with anti-Tyk2 and antiphosphotyrosine antibodies and by using an in vitro kinase assay. Analogous experiments were then performed with recombinant baculoviruses encoding constitutively active Jak family tyrosine kinases. In this case, p135tyk2, but not Jak-1 or Jak-2 protein, binds to the GST-IFN-R proteins, suggesting that the interaction between these two proteins is both direct and specific. We also demonstrate that Tyk2, from extracts of either IFN alpha-treated human cells or insect cells infected with the recombinant baculoviruses, can catalyze in vitro phosphorylation of GST-IFN-R protein in a specific manner. Deletion mutants of the GST-IFN-R protein were used to localize both the binding and tyrosine phosphorylation site(s) to a 46-amino-acid juxtamembrane region of the alpha subunit, which shows sequence homology to functionally similar regions of other cytokine receptor proteins. These data support the hypothesis that the Tyk2 protein functions as part of a receptor complex to initiate intracellular signaling in response to type I IFNs.

Differential tyrosine phosphorylation of the IFNAR chain of the type I interferon receptor and of an associated surface protein in response to IFN-alpha and IFN-beta

The human interferon alpha-receptor (IFNAR gene product) is a transmembranal protein of 557 amino acids with an intracytoplasmic domain of 100 amino acids containing four tyrosines. Antibodies to a C-terminal peptide (residues 521-536) were developed which efficiently immunoprecipitate the 105 kDa IFNAR protein from detergent extracts of human cells. We show that the IFNAR protein becomes tyrosine phosphorylated within 5 min after treatment of human myeloma U266 cells with IFN-alpha 2, IFN-alpha 8 or IFN-beta. The IFNAR chain interacts with both IFN-alpha 2 and IFN-beta, as demonstrated by cross-linking. Among elements involved in signal transduction by type I IFNs, the tyrosine kinase Tyk2 but not Jak1, and the ISGF3 transcription factor subunit Stat2 (p113) but not Stat1 (p91), are found associated with the IFNAR protein. After IFN-beta treatment for 5 min, a tyrosine-phosphorylated protein of approximately 95 kDa (beta-PTyr) is found bound to IFNAR, but can be dissociated by denaturation. The beta-PTyr protein is present on the cell surface, like IFNAR, as shown by extracellular biotin tagging. The ratio of beta-PTyr to IFNAR tyrosine phosphorylation is much higher with IFN-beta than with IFN-alpha 2 or 8. Both are IFN dependent and abrogated by a monoclonal antibody which blocks IFNAR action. The beta-PTyr component may represent an important difference in the action of IFN-beta as compared with IFN-alpha in their shared receptor system.

Direct binding to and tyrosine phosphorylation of the alpha subunit of the type I interferon receptor by p135tyk2 tyrosine kinase

Binding of type I interferons (IFNs) to their receptors induces rapid tyrosine phosphorylation of multiple proteins, including the alpha and beta subunits of the receptor, the polypeptides that form the transcriptional activator ISGF3 alpha (Stat113, Stat84, and Stat91), and the p135tyk2 and Jak-1 tyrosine kinases. In this report, we demonstrate that the alpha subunit of the type I IFN receptor (IFN-R) corresponds to the product of a previously cloned receptor subunit cDNA and, further, that the p135tyk2 tyrosine kinase directly binds and tyrosine phosphorylates this receptor subunit. Glutathione S-transferase (GST) fusion proteins encoding the different regions of the cytoplasmic domain of the alpha subunit can bind the p135tyk2 contained in human cell lysates. The association between the alpha subunit and Tyk2 was demonstrated by immunoblotting with anti-Tyk2 and antiphosphotyrosine antibodies and by using an in vitro kinase assay. Analogous experiments were then performed with recombinant baculoviruses encoding constitutively active Jak family tyrosine kinases. In this case, p135tyk2, but not Jak-1 or Jak-2 protein, binds to the GST-IFN-R proteins, suggesting that the interaction between these two proteins is both direct and specific. We also demonstrate that Tyk2, from extracts of either IFN alpha-treated human cells or insect cells infected with the recombinant baculoviruses, can catalyze in vitro phosphorylation of GST-IFN-R protein in a specific manner. Deletion mutants of the GST-IFN-R protein were used to localize both the binding and tyrosine phosphorylation site(s) to a 46-amino-acid juxtamembrane region of the alpha subunit, which shows sequence homology to functionally similar regions of other cytokine receptor proteins. These data support the hypothesis that the Tyk2 protein functions as part of a receptor complex to initiate intracellular signaling in response to type I IFNs.

Intrinsic ligand binding properties of the human and bovine alpha-interferon receptors

The Type I interferon receptor (IFN-alpha R) interacts with all IFN-alpha s, IFN-beta and IFN-omega, and seems to be a multisubunit receptor. To investigate the role of a cloned receptor subunit (IFN-alpha R1), we have examined the intrinsic ligand binding properties of the bovine and human IFN-alpha R1 polypeptides expressed in Xenopus laevis oocytes. Albeit with different efficiencies, Xenopus oocytes expressing either the human or bovine IFN-alpha R1 polypeptide exhibit significant binding and formation of crosslinked complexes with human IFN-alpha A and IFN-alpha B. Thus, the IFN-alpha R1 polypeptide most likely plays a direct role in ligand binding.

Generation and characterization of anti-idiotypic antibodies recognizing the interferon-alpha receptor: implications for ligand-receptor interactions

Monoclonal antibodies LI-1 and LI-8 against interferon-alpha A (IFN-alpha A) block IFN-alpha A activity and binding to its receptor, but they recognize distinct epitopes. Surprisingly, anti-idiotypic antibodies to both LI-1 and LI-8 have properties consistent with recognition of the receptor: anti-LI-1 and anti-LI-8 antibodies inhibit the binding of IFN-alpha A to its receptor. However, anti-LI-1 is an antagonist of IFN-alpha A, while anti-LI-8 is an agonist. Thus, at least some part of the epitopes on IFN-alpha A recognized by LI-1 and LI-8 are directly involved in receptor binding. Because these epitopes are spatially distinct, the implication is that the receptor binding site on IFN-alpha A must be extensive, or there are minimally two regions of IFN-alpha A involved in receptor interactions.

Tyrosine phosphorylation is required for activation of an alpha interferon-stimulated transcription factor

The signal transduction pathway of alpha interferon utilizes tyrosine phosphorylation to transmit a signal generated at the cell surface to the transcriptional machinery in the nucleus. Activation of the interferon pathway initiates with the binding of alpha interferon to its cell surface receptor. The ligand-receptor complex signals the activation of a latent cytoplasmic transcription factor. The active form of the interferon-stimulated gene factor (ISGF3) is phosphorylated on tyrosine residues. ISGF3 subsequently translocates to the nucleus and binds to a DNA sequence, the interferon-stimulated response element, found within the promoter of inducible genes. ISGF3 is a multicomponent factor consisting of four proteins of 113 kDa, 91 kDa, 84 kDa, and 48 kDa. Three proteins consistent with sizes of 113 kDa, 91 kDa, and 84 kDa copurify with ISGF3 and are phosphorylated on tyrosine residues after stimulation by alpha interferon. Tyrosine phosphorylation is essential for activation of ISGF3. Genistein, a tyrosine kinase inhibitor, blocks the appearance of ISGF3 and blocks the transcriptional stimulation of interferon-induced genes. This study shows that tyrosine phosphorylation provides a link between the interferon-receptor complex at the plasma membrane and specific activation of gene expression in the nucleus.

Expression of the IFN alpha receptor in hairy cell leukaemia

The expression of IFN alpha receptors on the surface of hairy cell leukaemia cells was studied using affinity crosslinking methods, flow cytometry with a recently produced anti-IFN alpha receptor monoclonal antibody (IFNaR3), and binding techniques. IFN alpha receptors were detected by flow cytometry and affinity crosslinking in eight cases showing a normal receptor structure with 125I-IFN alpha 2-receptor complexes with molecular weights of 210, 130 and 110 kD. The hairy cell leukaemia cells from one patient did not express IFN alpha receptors as determined by flow cytometry, affinity crosslinking and binding studies. Northern blot analysis showed expression of mRNA for the gene coding for the putative IFN alpha receptor in all cases studied, including the patient with lack of IFN alpha receptor expression on hairy cells. This patient was refractory to IFN alpha 2 treatment. Our data suggest that lack of expression of IFN alpha receptors in rare cases may be associated with refractoriness to IFN alpha 2 therapy.

Contrasting effects of alpha, beta, and gamma interferons on nonspecific suppressor function in multiple sclerosis

Interferons are biological molecules with antiviral, antiproliferative, and immunomodulatory actions. Interferon alpha (IFN-alpha) and -beta are potentially useful in the treatment of multiple sclerosis (MS). IFN-gamma, in contrast, increases the frequency of exacerbations of MS. In this study, we compared the effect of recombinant human IFN-alpha, -beta, and -gamma on suppressor function in patients with MS. Nonspecific suppressor cell function, measured in a concanavalin A suppressor assay, was significantly decreased in 16 patients with progressive MS (mean percent suppression +/- SEM, 14.4 +/- 5.5 in patients with MS, 33.5 +/- 4.8 in 16 normal subjects; p less than 0.001). Recombinant human IFN-beta augmented suppressor function in MS to 45.4 +/- 5.1% (p less than 0.001) and in control subjects to 56.8 +/- 3.8% (p less than 0.001). Similarly, recombinant human IFN-alpha improved suppression in MS to 43.0 +/- 5.6% (p less than 0.001) and in control subjects to 51.1 +/- 5.9% (p less than 0.001). In contrast, recombinant human IFN-gamma had no effect on suppressor function in patients with MS and in control subjects. This study shows that IFN-alpha and -beta augment deficient suppressor function in MS, whereas IFN-gamma has no effect on suppressor function in the progressive phase of the disease.