Molecular characterization of the murine interferon γ receptor cDNA

Interferons and Their Receptors in Birds: A Comparison of Gene Structure, Phylogenetic Analysis, and Cross Modulation

Interferon may be thought of as a key, with the interferon receptor as the signal lock: Crosstalk between them maintains their balance during viral infection. In this review, the protein structure of avian interferon and the interferon receptor are discussed, indicating remarkable similarity between different species. However, the structures of the interferon receptors are more sophisticated than those of the interferons, suggesting that the interferon receptor is a more complicated signal lock system and has considerable diversity in subtypes or structures. Preliminary evolutionary analysis showed that the subunits of the interferon receptor formed a distinct clade, and the orthologs may be derived from the same ancestor. Furthermore, the development of interferons and interferon receptors in birds may be related to an animal’s age and the maintenance of a balanced state. In addition, the equilibrium between interferon and its receptor during pathological and physiological states revealed that the virus and the host influence this equilibrium. Birds could represent an important model for studies on interferon’s antiviral activities and may provide the basis for new antiviral strategies.

IFN-γ and its receptors in a reptile reveal the evolutionary conservation of type II IFNs in vertebrates

In this study, interferon gamma (IFN-γ) and interferon gamma receptor (IFN-γR) genes have been identified in non-avian reptile, the North American green anole lizard (Anolis carolinensis). Like their counterparts from other jawed vertebrates, lizard IFN-γ, IFN-γR1 and IFN-γR2 show conserved features in genomic organizations, gene loci and protein sequences. The IFN-γ gene has the full cDNA sequence of 936 bp, with 522 bp open reading frame (ORF) encoding 174 amino acids, and has the genomic organization of four exons and three introns as observed in IFN-γ genes of other classes of vertebrates. The receptors, IFN-γR1 and IFN-γR2 have the ORF of 1278 and 984 bp, coding for 425 and 327 aa, respectively, with the genome organization of seven exons and six introns. In the gene loci of IFN-γ, DYRK2, IL22, IL26 and MDM1 are found with conserved synteny in vertebrates, and similar genes adjacent to IFN-γR1 and IFN-γR2 were also found. These receptors also contain conserved motifs, such as the membrane-proximal region and the C-terminal five residue motif in IFN-γR1, and intracellular conservative sequence in IFN-γR2, which have been confirmed to mediate down-stream JAK-STAT signaling pathway in mammals. IFN-γ and its receptors, IFN-γR1 and IFN-γR2 were constitutively expressed in organs/tissues examined in the lizard, and up-regulated expression of IFN-γ was observed in organs/tissues examined following the poly(I:C) stimulation, suggesting its antiviral role in lizards. The conserved features of IFN-γ and its receptors, IFN-γR1 and IFN-γR2, in gene organization and gene locus as well as in functional domain or motif may imply that the function of type II IFN system is evolutionarily conserved in the green anole lizard, as observed in other classes of vertebrates.

Genomic structure and characterization of mRNA expression pattern of porcine interferon gamma receptor 1 gene

Interferon gamma receptor (IFNGR) plays an important role in the biological effects of IFN-γ. In this study, porcine IFNGR1 cDNA was cloned and two transcripts both having a coding region of 1413 bp were identified. Porcine IFNGR1 cDNA shares 62.95%, 63.73%, 72.90% and 81.10% identity in nucleotide sequence; and 45.64%, 46.69%, 58.04% and 72.55% homology in amino acid sequence to those of rat, mouse, human and cattle, respectively. The porcine IFNGR1 genomic structure consists of seven exons and six introns and is located on porcine chromosome 1. The mRNA expression of porcine IFNGR1 gene is detected in all tissues examined, with strong expression in spleen and liver tissues and weak expression in cerebrum, cerebellum and uterus tissues, respectively. A different developmental pattern in IFNGR1 mRNA expression between Laiwu and Duroc breeds was revealed by real-time quantitative RT-PCR: in Duroc pigs, a significantly higher expression was found in the tissues of heart (P<0.05), liver (P<0.01), kidney (P<0.01) and skeletal muscle (P<0.05) of adult pigs compared to piglets. In porcine reproductive and respiratory syndrome virus (PRRSV)-infected Dapulian pigs, compared to the uninfected ones, the expression level of IFNGR1 mRNA in spleen was significantly up-regulated (P<0.05), whereas its expression in the lymph node was significantly down-regulated (P<0.05); in PRRSV-infected Duroc × Yorkshire × Landrace commercial pigs, however, the differences both in spleen and lymph node tissues were not significant.

Human BLyS facilitates engraftment of human PBL derived B cells in immunodeficient mice

The production of fully immunologically competent humanized mice engrafted with peripheral lymphocyte populations provides a model for in vivo testing of new vaccines, the durability of immunological memory and cancer therapies. This approach is limited, however, by the failure to efficiently engraft human B lymphocytes in immunodeficient mice. We hypothesized that this deficiency was due to the failure of the murine microenvironment to support human B cell survival. We report that while the human B lymphocyte survival factor, B lymphocyte stimulator (BLyS/BAFF) enhances the survival of human B cells ex vivo, murine BLyS has no such protective effect. Although human B cells bound both human and murine BLyS, nuclear accumulation of NF-κB p52, an indication of the induction of a protective anti-apoptotic response, following stimulation with human BLyS was more robust than that induced with murine BLyS suggesting a fundamental disparity in BLyS receptor signaling. Efficient engraftment of both human B and T lymphocytes in NOD rag1^−/− Prf1^−/− immunodeficient mice treated with recombinant human BLyS is observed after adoptive transfer of human PBL relative to PBS treated controls. Human BLyS treated recipients had on average 40-fold higher levels of serum Ig than controls and mounted a de novo antibody response to the thymus-independent antigens in pneumovax vaccine. The data indicate that production of fully immunologically competent humanized mice from PBL can be markedly facilitated by providing human BLyS.

Molecular cloning and characterization of chicken interferon-gamma receptor alpha-chain

In this study, a cDNA sequence of Huiyang chicken interferon-gamma (IFN-gamma) receptor alpha-chain (chIFNGR-1) gene wasgenerated using rapid amplification of cDNA ends (RACE) method for the first time. The predicted 422 amino acids showed approximately 25%-29% sequence identity and 53%-55% similarity to mammalian homologues. There are two fibronectin type-III (FN-III) domains of about 110 residues in the extracellular domain, and LPKS and YDKPH motifs in the intracellular domain, which are conserved in the mammalian IFNGR-1 as the binding sites of JAK1 and STAT1. Expression analysis by Northern blot revealed that the chIFNGR-1 was highly expressed in spleen, thymus, peripheral blood lymphocytes (PBLs), lung, cecum tonsil, and liver. The extracellular region of chIFNGR-1 (chIFNGR-1EC) was expressed in Escherichia coli and purified. The purified IFNGR-1EC was further characterized by mass spectroscopy and circular dichroism (CD) spectroscopy. The molecular weight of the recombinant chIFNGR-1EC (rchIFNGR-1EC) was measured as 24 364 Da, and its secondary structure contained 17.6% alpha-helix, 36.4% beta-sheet, 17.2% turn, and 28.8% random coil. Furthermore, three-dimensional modeling presented the most probable structure of chIFNGR-1EC. These * ndings show that the identified chicken cDNA sequence encodes an IFNGR1 homologue, and the chIFNGR-1EC resembles the similar structure with other IFN receptors.

Historical developments in the research of interferon receptors

Interferons (IFNs) were discovered 50 years ago independently by Isaacs and Lindemann and by Nagata and Kojima. When it was later realized that IFNs are active at very low concentrations, research began to determine how their powerful effects were generated from such a small initial signal. It has since been established that interferons, as well as all other cytokines, employ cell surface receptors to translate their presence in the serum to a potent cellular response to a viral infection. These receptor complexes are composed of multiple distinct glycosylated transmembrane polypeptides, a number of protein tyrosine kinases, and interact transiently with a large variety of other proteins including transcription factors, phosphatases, signaling repressors, and adaptor proteins coupling the receptor to alternative signaling pathways. Three major receptor complexes exist that are exclusive to each of three major classes of interferon. Even though the effects of each major class of interferon vary physiologically, each receptor complex interacts with its ligand in similar ways and activates similar signaling cascades. In this mini-review, we take a historical perspective at the major events in the characterization of interferon receptors, discussing interesting results that still need to be explained.

Evolution of the Class 2 cytokines and receptors, and discovery of new friends and relatives

The sequencing of a wide variety of genomes and their transcripts has allowed researchers to determine how proteins or protein families evolved and how strongly during evolution a protein has been conserved. In this report, we analyze the evolution of the Class 2 ligands and their cognate receptors by analyzing Class 2 ligand and receptor chain gene sequences from a variety of DNA sequence databases. Both the Class 2 cytokines and receptor chains appear to have developed during the evolution of the chordate phyla: distant homologues of type I interferon (IFN) receptors are the only Class 2 cytokine receptors identified in the Ciona genomes, while a wide variety of Class 2 ligands and receptor chains are encoded in the currently available genomes of bony vertebrates (teleost fish, amphibians, reptiles, birds, mammals). Phylogenetic trees of ligands and ligand-binding receptor chains demonstrate that proteins involved in conferring antiviral activity diverged before those involved in adaptive immunity. Genes encoding IFNs and IFN receptors duplicated multiple times during chordate evolution, suggesting that duplication of genes encoding IFN activity conveyed an evolutionary advantage. Altogether, these data support a model whereby the original Class 2 cytokines and receptors evolved and duplicated during the evolution of the chordate innate immune response system; new receptor and ligand duplications evolved into signaling molecules to fulfill communication requirements of a highly specialized and differentiated vertebrate immune system. In addition, the genomic analysis led to the discovery of some new members of this family.

Mouse oocytes and preimplantation embryos bear the two sub-units of interferon-gamma receptor

Cytokines and growth factors play important roles in implantation and maintenance of pregnancy, but also during early development. Among them interferon-gamma (IFNgamma) is highly expressed by mammalian trophoblast cells during implantation and seems to be involved in some cases of pregnancy loss. In the present study we investigated the possible presence of IFNgamma receptors (IFNGR) on mouse oocytes and preimplantation embryos. The two receptor chains IFNgammaRalpha (IFNGR-1) and IFNgammaRbeta (IFNGR-2) have been detected by indirect immunofluorescence at the surface of mouse oocytes (in germinal vesicle and metaphase II stages), as well as at all stages of in vitro embryo development from the one-cell to blastocyst stage. IFNGR appeared to colocalize partly with ganglioside GM1 at the cell surface of oocytes and embryos, indicating a possible preferential localization of this receptor in "rafts" microdomains. This was analyzed in more detail using software developed in the laboratory. IFNgamma was found to bind to its receptor at all stages analyzed. RT-PCR and Southern blot experiments confirmed the presence of the transcriptionally regulated IFNGR-2 chain mRNA, in mouse oocytes and preimplantation embryos. These results show, for the first time, that mouse oocytes and preimplantation embryos bear a complete and theoretically functional IFNGR, suggesting that this cytokine could play a role during early development.

Biologic functions of the IFN-gamma receptors

Interferon-gamma (IFN-gamma) is a cytokine that plays an important role in inducing and modulating an array of immune responses. Cellular responses to IFN-gamma are mediated by its heterodimeric cell-surface receptor (IFN-gammaR), which activates downstream signal transduction cascades, ultimately leading to the regulation of gene expression. In order to study the role of IFN-gamma in a number of immune responses and pathways, researchers have generated mice with altered patterns of IFN-gammaR gene expression. These studies, together with analyses of naturally occurring mutations of the IFN-gammaR in man, have been instrumental in elucidating the diverse functions of IFN-gamma, and are the subject of this review.

Introduction of protein kinase recognition sites into proteins: a review of their preparation, advantages, and applications

Labeled proteins are used in a variety of applications. This review focuses on methods that utilize genetic engineering to introduce protein kinase recognition sites into proteins. Many protein kinase recognition sites can be introduced into proteins and serve as useful tags for a variety of purposes. The introduction of protein kinase recognition sites into proteins can be achieved without modifying the essential structure or function of the proteins. Because proteins modified by these procedures retain their activity after phosphorylation, they can be used in many applications. The phosphorylatable proteins can be labeled easily to high specific activity with radioisotopes ((32)P, (33)P, or (35)S), or the nonradioactive (31)P can be used. The use of these radioisotopes provides a convenient and safe method for radiolabeling proteins. Moreover, the use of the nonradioactive (31)P with protein tyrosine kinase recognition sites permits the tagging of proteins and their detection with the many anti-phosphotyrosine antibodies available. Overall, the procedure represents a convenient, safe, and efficient method to label proteins for a variety of applications.

Altered cytokine (receptor) mRNA expression as a tool in immunotoxicology

Molecular immunotoxicology is aimed at analysing exposure effects on the temporal expression of important immunoregulatory genes. Cytokines play key roles in the immune system and thus molecular immunotoxicology has focused on the analysis of cytokine (expression) levels. These targets offer important new avenues to explore both in terms of mechanistic understanding of immunotoxicity and in terms of developing new assays and tests for predicting the immunotoxic potential of novel compounds. Effects on cytokine levels can be analysed on two different levels, these being mRNA and protein. The choice essentially depends on the aim of the study. Proteins comprise the biological activity so they are a more direct measure than mRNA. mRNA on the other hand, measures at a specific point in time within a tissue or organ, whereas protein is measured in a body fluid, possibly as a spill-over from tissue, or in a supernatant as a summation over a culture period. mRNA levels are assayed using Northern or dot blotting that both comprise hybridisation and using reverse transcription-polymerase chain reaction (RT-PCR). Although the latter technique has both enormous sensitivity and relative ease of operation as important advantages, it requires much more effort in terms of quantitation. References to the nucleic acid sequences of human, murine, and rat cytokines and their receptors are presented (with accession numbers). Examples in which molecular techniques were successfully employed to assess immunotoxicity and (in some cases) understand mechanisms of action are also presented.

Identification and regulation of testicular interferon-gamma (IFNgamma) receptor subunits: IFNgamma enhances interferon regulatory factor-1 and interleukin-1beta converting enzyme expression

Interferon-gamma (IFNgamma) transmits its signal through a specific cell surface receptor (IFNgammaR), which consists of a primary ligand binding alpha-chain (IFNgammaR alpha) and a signaling beta-chain (IFNgammaR beta). Recent studies identified the cytokines IFNgamma, interleukin-6 (IL-6), IL-1alpha, and tumor necrosis factor-alpha in testicular cells. Therefore, we: 1) examined the expression of IFNgammaR alpha and IFNgammaR beta subunits in freshly isolated and purified rat testicular cells; 2) examined the differential regulation of receptor components by cytokines using primary cultures of Sertoli cells; 3) identified the cell signaling pathway components of testicular IFNgammaR; and 4) characterized the functional role of testicular IFNgamma using primary Sertoli cells. We demonstrated the messenger RNAs for both chains of IFNgammaR in rat testicular cells using Northern hybridization analysis. Western blot analysis and immunocytochemistry showed that both specific IFNgammaR protein subunits were present in cultured primary Leydig and Sertoli cells prepared from the testes of immature rats. The expression of both IFNgammaR component messenger RNAs in cultured Sertoli cells was increased by its specific ligand (IFNgamma), as well as IL-1alpha and tumor necrosis factor-alpha, in both a time- and dose-dependent manner. IFNgamma-activation of the Janus (JAK) tyrosine kinases, JAK1 and JAK2 proteins, indicate that IFNgammaR, expressed in the Sertoli cell, is functional. Moreover, IFNgamma modulates the expression of interferon regulatory factor (IRF)-1 and IL-1beta converting enzyme genes in Sertoli cells. Thus, our data are suggestive of a role(s) for IFN-gamma in the regulation of distinct gene expression and cell-specific sensitivity to apoptosis in the testis.

The interferon gamma (IFN-gamma) receptor: a paradigm for the multichain cytokine receptor

With the purification and cloning of the interferon gamma (IFN-gamma) receptor chains the mechanism of IFN-gamma action and the resultant signal transduction events were delineated in remarkable detail. The interferon gamma (IFN-gamma) receptor complex consists of two chains: IFN-gammaR1, the ligand-binding chain, and IFN-gammaR2, the accessory chain. Binding of IFN-gamma causes oligomerization of the two IFN-gamma receptor subunits, IFN-gammaR1 and IFN-gammaR2, which initiates the signal transduction events: activation of Jak1 and Jak2 receptor associated protein tyrosine kinases, phosphorylation of the IFN-gammaR1 intracellular domain on Tyr440 followed by phosphorylation and activation of Stat1alpha, the latent transcriptional factor. With all these steps established, the IFN-gamma receptor complex has provided the basic model for understanding the receptors for other members of the family of class II cytokine receptors.

THE IFNγ RECEPTOR:A Paradigm for Cytokine Receptor Signaling

▪ Abstract  During the last several years, the mechanism of IFNγ-dependent signal transduction has been the focus of intense investigation. This research has recently culminated in the elucidation of a comprehensive molecular understanding of the events that underlie IFNγ-induced cellular responses. The structure and function of the IFNγ receptor have been defined. The mechanism of IFNγ signal transduction has been largely elucidated, and the physiologic relevance of this process validated. Most recently, the molecular events that link receptor ligation to signal transduction have been established. Together these insights have produced a model of IFNγ signaling that is nearly complete and that serves as a paradigm for signaling by other members of the cytokine receptor superfamily.

Chimeric erythropoietin-interferon gamma receptors reveal differences in functional architecture of intracellular domains for signal transduction

Binding of interferon gamma (IFN-gamma) causes oligomerization of the two interferon gamma receptor (IFN-gammaR) subunits, receptor chain 1 (IFN-gammaR1, the ligand-binding chain) and the second chain of the receptor (IFN-gammaR2), and causes activation of two Jak kinases (Jak1 and Jak2). In contrast, the erythropoietin receptor (EpoR) requires only one receptor chain and one Jak kinase (Jak2). Chimeras between the EpoR and the IFN-gammaR1 and IFN-gammaR2 chains demonstrate that the architecture of the EpoR and the IFN-gammaR complexes differ significantly. Although IFN-gammaR1 alone cannot initiate signal transduction, the chimera EpoR/gammaR1 (extracellular/intracellular) generates slight responses characteristic of IFN-gamma in response to Epo and the EpoR/gammaR1. EpoR/gammaR2 heterodimer is a fully functional receptor complex. The results demonstrate that the configuration of the extracellular domains influences the architecture of the intracellular domains.

The IFN gamma receptor: a paradigm for cytokine receptor signaling

During the last several years, the mechanism of IFN gamma-dependent signal transduction has been the focus of intense investigation. This research has recently culminated in the elucidation of a comprehensive molecular understanding of the events that underlie IFN gamma-induced cellular responses. The structure and function of the IFN gamma receptor have been defined. The mechanism of IFN gamma signal transduction has been largely elucidated, and the physiologic relevance of this process validated. Most recently, the molecular events that link receptor ligation to signal transduction have been established. Together these insights have produced a model of IFN gamma signaling that is nearly complete and that serves as a paradigm for signaling by other members of the cytokine receptor superfamily.

The intracellular domain of the second chain of the interferon-gamma receptor is interchangeable between species

In this report we show that the mouse interferon (IFN)-gamma R1 and IFN-gamma R2 subunits expressed in hamster cells are capable of rendering the cells sensitive to mouse IFN-gamma as measured by induction of class I MHC antigens and the activation of the transcription factor Stat1 alpha. However, these cells showed no antiviral protection in response to IFN-gamma when challenged with vesicular stomatitis virus (VSV) but limited protection when challenged with encephalomyocarditis virus (EMCV). Furthermore, the cytoplasmic domains of the IFN-gamma R2 subunits, like the cytoplasmic domains of the IFN-gamma R1 chains, can be interchanged between species with no loss of biologic activity, demonstrating that the species-specific interaction of the IFN-gamma R1 and IFN-gamma R2 chains involves only the extracellular domains of the two proteins.

The structure of the gene for the second chain of the human interferon-gamma receptor

The gene for the second chain of the human interferon-gamma receptor was analyzed from cosmid DNA clones. The gene spans over 33 kilobases of DNA and contains seven exons. The signal peptide is encoded by exons 1 and 2, the extracellular domain by exons 2, 3, 4, 5, and by part of 6. Exon 6 also encodes the whole transmembrane domain and part of the intracellular domain. Exon 7 encodes the remainder of the intracellular domain and contains the 3'-untranslated region. The sequences at the exon/intron boundaries are well conserved with respect to canonical acceptor/donor sites (AG/GT). The 5'-flanking region was sequenced and analyzed for transcription factor binding sites. No TATA or CAAT boxes in the promoter region were identified. Consistent with the lack of a TATA box, analysis of the mRNAs by primer extension showed multiple transcription start sites. Promoter activity of the 5'-flanking region was investigated with a luciferase reporter gene and the cytomegalovirus minimal promoter. Segments of the 5' region with promoter activity were identified.

In Xenopus oocytes the human C3a and C5a receptors elicit a promiscuous response to the anaphylatoxins

The Xenopus laevis oocyte has been widely utilized for cloning and functional expression of G-protein coupled receptors (GPCR). This system was used for the functional expression and characterization of the recently identified human C3a receptor. Complementary RNA from the human C3a receptor was transcribed in vitro and microinjected into Xenopus oocytes for functional characterization. A positive response to a synthetic C3a peptide agonist and to C3a, but not to platelet activating factor or fMetLeuPhe was detected. In addition, a response of approximately one third the amplitude obtained with C3a was obtained with rC5a. Conversely, oocytes co-injected with the C5a receptor and total RNA isolated from U937 cells responded to C5a as well as to C3a and the C3a synthetic peptide. A functional response with the anaphylatoxin C3a receptor in oocytes was dependent on co-injection of a pertussis toxin sensitive complementary human factor which could be supplied by co-injection of total RNA isolated from U937 cells. Oocytes expressing the anaphylatoxin C3a and C5a receptors responded to both agonists, in each case the response to the cognate ligand was substantially more robust than the response elicited by the other anaphylatoxin.

Other kinases can substitute for Jak2 in signal transduction by interferon-gamma

Each cytokine which utilizes the Jak-Stat signal transduction pathway activates a distinct combination of members of the Jak and Stat families. Thus, either the Jaks, the Stats, or both could contribute to the specificity of ligand action. With the use of chimeric receptors involving the interferon gamma receptor (IFN-gammaR) complex as a model system, we demonstrate that Jak2 activation is not an absolute requirement for IFN-gamma signaling. Other members of the Jak family can functionally substitute for Jak2. IFN-gamma can signal through the activation of Jak family members other than Jak2 as measured by Statlalpha homodimerization and major histocompatibility complex class I antigen expression. This indicates that Jaks are interchangeable and indiscriminative in the Jak-Stat signal transduction pathway. The necessity for the activation of one particular kinase during signaling can be overcome by recruiting another kinase to the receptor complex. The results may suggest that the Jaks do not contribute to the specificity of signal transduction in the Jak-Stat pathway to the same degree as Stats.

Identification of an interferon-gamma receptor alpha chain sequence required for JAK-1 binding

We have shown previously that a four-amino acid block residing at positions 266-269 (LPKS) in the intracellular domain of the human interferon-gamma (IFN-gamma) receptor alpha chain is critical for IFN-gamma-dependent tyrosine kinase activation and biologic response induction. Herein we show that this sequence is required for the constitutive attachment of the tyrosine kinase JAK-1. Using a vaccinia expression system, a receptor alpha chain-specific monoclonal antibody coprecipitated JAK-1 from cells coexpressing JAK-1 and either (a) wild type IFN-gamma receptor alpha chain, (b) a receptor alpha chain truncation mutant containing only the first 59 intracellular domain amino acids, or (c) a receptor mutant containing alanine substitutions for the functionally irrelevant residues 272-275. In contrast, JAK-1 was not coprecipitated when coexpressed with a receptor alpha chain mutant containing alanine substitutions for the functionally critical residues 266-269 (LPKS). Mutagenesis of the LPKS sequence revealed that Pro-267 is the only residue obligatorily required for receptor function. In addition, Pro-267 is required for JAK-1 binding. These results thus identify a site in the IFN-gamma receptor alpha chain required for constitutive JAK-1 association and establish that this association is critical for IFN-gamma signal transduction.

Growth hormone, interferon-gamma, and leukemia inhibitory factor promoted tyrosyl phosphorylation of insulin receptor substrate-1

The identification of JAK2 as a growth hormone (GH) receptor-associated, GH-activated tyrosine kinase has established tyrosyl phosphorylation as a signaling mechanism for GH. In the present study, GH is shown to stimulate tyrosyl phosphorylation of insulin receptor substrate 1 (IRS-1), the principle substrate of the insulin receptor. Tyrosyl phosphorylation of IRS-1 is a critical step in insulin signaling and provides binding sites for proteins with the appropriate Src homology 2 domains, including the 85-kDa regulatory subunit of phosphatidylinositol (PI) 3'-kinase. In 3T3-F442A fibroblasts, GH-dependent tyrosyl phosphorylation of IRS-1 was detected by 1 min and at GH concentrations as low as 5 ng/ml (0.23 nM). Tyrosyl phosphorylation of IRS-1 was transient, with maximal stimulation detected at 30 min and diminished signal detected at 60 min. The ability of GH receptor (GHR) to transduce the signal for IRS-1 tyrosyl phosphorylation is mediated by the intracellular region of GHR between amino acids 295 and 380 by a mechanism not involving the two tyrosines in this region. This region of GHR is required for GH-dependent JAK2 association and activation (VanderKuur, J. A., Wang, X., Zhang, L., Campbell, G. S., Allevato, G., Billestrup, N., Norstedt, G., and Carter-Su, C. (1994) J. Biol. Chem. 269, 21709-21717). When other cytokines that activate JAK2 were tested for the ability to stimulate the tyrosyl phosphorylation of IRS-1, stimulation was detected with interferon-gamma and leukemia inhibitory factor. The correlation between JAK2 tyrosyl phosphorylation and IRS-1 tyrosyl phosphorylation in response to GH, interferon-gamma, and leukemia inhibitory factor and in cells expressing different GHR mutants, provides evidence that IRS-1 may interact with JAK2 or an auxiliary molecule that binds to JAK2. GH is also shown to stimulate binding of IRS-1 to the 85-kDa regulatory subunit of PI 3'-kinase. The ability of GH to stimulate tyrosyl phosphorylation of IRS-1 and its association with PI 3'-kinase provides a biochemical basis for responses shared by insulin and GH including the well characterized insulin-like metabolic effects of GH observed in a variety of cell types.

Characterization of the 5' flanking region and gene encoding the mouse interferon-gamma receptor

The purpose of this investigation was to characterize the gene that encodes the receptor for mouse interferon-gamma (IFN-gamma R), including determination of its size, intronic boundaries and its transcription start points (tsp). The mouse IFN-gamma R gene is 22-kb long, with six introns that range in size from approx. 1 to 7 kb. The first six exons encode the extracellular and transmembrane (TM) domains of the protein, while the last exon of about 1 kb encodes most of the intracellular domain. No canonical TATA box can be found in the 5' flanking sequence of the gene, and primer extension analysis indicates multiple tsp. In addition, the gene's 5' promoter region was sequenced to identify candidate responsive elements that might regulate expression of the gene. Among the putative regulatory motifs identified by computer-assisted analysis are multiple SP1 and AP-2 sites, an NF1 and CCAAT box, as well as a potential cyclic AMP-responsive element (CRE).

Mechanisms of viral inhibition by interferons

Interferons (IFNs) are a family of related proteins grouped in four species (alpha, beta, gamma and omega) according to their cellular origin, inducing agents and antigenic and functional properties. Their binding to specific receptors leads to the activation of signal transduction pathways that stimulate a defined set of genes, whose products are eventually responsible for the IFN antiviral effects. Their action against viruses is a complex phenomenon. It has been reported that IFNs restrict virus growth at the levels of penetration, uncoating, synthesis of mRNA, protein synthesis and assembly. This review will attempt to evaluate evidence of the involvement of the IFN-inducible proteins in the expression of the antiviral state against RNA or DNA viruses.

Structural elements required for receptor recognition of human interferon-gamma

Interferon (IFN)-gamma is a central factor in numerous immune responses. Recently the three-dimensional structure of human and rabbit IFN-gamma has been elucidated. This review attempts to bring together the structure and function information into a working model of IFN-gamma: receptor interaction. Based on mutagenesis studies, and corroborated by work with peptides, antibodies and proteolytic digestion, three regions have been found to be important for receptor binding: a long loop connecting the A and B helices, His111 in the F helix and a conserved section of the flexible carboxyl terminus. These three regions may form one continuous binding domain.

First trimester human trophoblast expresses both interferon-gamma and interferon-gamma-receptor

Interferon-gamma (IFN-gamma) is a lymphokine, produced by activated T lymphocytes, which plays a key regulatory role in the host immunological responses. In addition, IFN-gamma is expressed by human and porcine trophoblast. As IFN-gamma exerts its biological functions through specific cell surface receptors and a great number of IFN-gamma receptors (IFN-gamma R) have been purified from human placenta, we have examined the relative distribution of IFN-gamma and IFN-gamma R in human placental tissues at different stages of pregnancy. By using immunohistochemical analysis and monoclonal antibodies, it was found that IFN-gamma expression is intense in the first trimester but almost imperceptible at term, whereas the expression of IFN-gamma R is present at both stages of pregnancy. For both lymphokine and receptor, the most intense expression was observed in villous syncytiotrophoblast and in extravillous interstitial trophoblast. From these results it appears that the expression of IFN-gamma R in trophoblast is related to the presence of the lymphokine in the early phase of gestation but not later. On this basis, it can be argued that IFN-gamma exerts its functional role via an autocrine and/or a paracrine loop mainly during the first trimester.

Identification and sequence of an accessory factor required for activation of the human interferon gamma receptor

Human chromosomes 6 and 21 are both necessary to confer sensitivity to human interferon gamma (Hu-IFN-gamma), as measured by induction of class I human leukocyte antigen (HLA) and protection against encephalomyocarditis virus (EMCV) infection. Whereas human chromosome 6 encodes the Hu-IFN-gamma receptor, human chromosome 21 encodes accessory factors for generating biological activity through the Hu-IFN-gamma receptor. Probes from a genomic clone were used to identity cDNA clones expressing a species-specific accessory factor. These cDNA clones are able to substitute for human chromosome 21 to reconstitute the Hu-IFN-gamma receptor-mediated induction of class I HLA antigens. However, the factor encoded by the cDNA does not confer full antiviral protection against EMCV, confirming that an additional factor encoded on human chromosome 21 is required for reconstitution of antiviral activity against EMCV. We conclude that this accessory factor belongs to a family of such accessory factors responsible for different actions of IFN-gamma.

Expression of the interferon-gamma receptor gene in mouse placentas is related to stage of gestation and is restricted to specific subpopulations of trophoblast cells

In order to evaluate the potential of placental cells to bind the multifunctional cytokine, interferon-gamma (IFN-gamma), tissues collected from pregnant Swiss mice were analysed for IFN-gamma receptor (IFN-gamma R) mRNA and protein. Northern blot hybridization studies indicated that the relative abundance of IFN-gamma R mRNA increased as gestation progressed to term. Analysis by in situ hybridization revealed that trophoblast cells first contained high steady state levels of IFN-gamma R mRNA at g.d. 12. At g.d. 12 and 14, transcription was restricted to cells in the spongiotrophoblast region and nests of similar cells in the labyrinthine region. These cells also contained immunoreactive IFN-gamma R protein. By g.d. 18, IFN-gamma R mRNA was clearly detectable in large spongiotrophoblast cells and labyrinthine trophoblast. IFN-gamma R mRNA was low to absent in giant trophoblast cells at all stages of gestation. Specific mRNA was present in parietal and visceral yolk sac cells by g.d. 14. Thus, expression of the IFN-gamma R gene in mouse placental cells is influenced by stage of gestation, cell lineage and state of differentiation. Whether or not these cells respond vigorously to IFN-gamma with induction of antiviral proteins, increased MHC class I antigens and growth modulation may therefore be determined by their expression of specific receptors for this pluripotent cytokine.

Modulation of murine and human interferon-gamma receptor expression by their ligands or phorbol ester

IFN-gamma receptor expression on murine leukaemic L1210-cells has been studied. With the help of a transfected cell-line expressing the heterologous human receptor it was possible to discern receptor-specific properties like internalization from those regulating their expression on the surface. Recombinant IFN-gamma binds specifically to its homologous receptor at 4 degrees C and is rapidly internalized at physiologic temperatures. For this effect to occur, ligand binding to its receptor at 37 degrees C is necessary and sufficient. This notion is confirmed since a reduction in the number of heterologous human IFN-gamma receptors on the murine cell surface occurred exclusively after treatment with human IFN-gamma. Even weak doses of ligand, insufficient to occupy all receptors, led to a pronounced disappearance of binding sites. However, both receptors are simultaneously up-regulated in the presence of TPA, indicating a separate pathway which is not species-specific. Our findings imply that similar elements of the intracellular signal transduction machinery are involved in the control of MuIFN-gamma and HuIFN-gamma receptor expression. The results indicate also that factors involved in binding, internalization, and regulation of receptor gene expression are not species-specific.

Immunomodulation with soluble IFN-gamma receptor: preliminary study

Several in vivo experiments support the hypothesis that an IFN-gamma antagonist may have therapeutic applications in autoimmune diseases, hypersensitivities, and alloreactions. IFN-gamma exerts its biological activity through the binding to a single-chain cell surface receptor. The protein that corresponds to the external domain of mouse IFN-gamma receptor was expressed in insect cells infected with recombinant baculovirus; this protein was characterized and used in vivo as a prototype of the IFN-gamma antagonist. This protein does not show any strong antigenicity after in vivo injection in mice. Despite a blood half-life of only 1-3 hr as demonstrated in pharmacokinetic experiments, the mouse soluble IFN-gamma R was able to modify the onset of acute GVHD (alloreaction) and chronic GVHD (lupuslike disease).

Analysis of soluble human and mouse interferon-gamma receptors expressed in eukaryotic cells

The extracellular domains of the human and mouse interferon-gamma receptors were produced in insect Spodoptera frugiperda cells infected with recombinant baculoviruses and in mammalian Chinese-hamster-ovary cells. The receptors expressed in both systems are secreted into the culture medium. Their signal peptides are cleaved off and the proteins show heterogeneity in glycosylation which, however, does not affect the capacity to bind interferon gamma or specific antibodies. The soluble mouse receptors exhibit binding capacities similar to those of cell-surface-anchored receptors, whereas the human receptors exhibit a lower binding capacity. All soluble receptors inhibit the binding of interferon gamma to cellular receptors and neutralize the antiviral activity exerted by interferon gamma. These receptors could therefore be useful for structure/function analyses and in vivo studies.

Encoding of a homolog of the IFN-gamma receptor by myxoma virus

Many poxvirus-encoded virulence factors have been identified as proteins that are secreted from infected cells. The major secreted protein (37 kilodaltons) from cells infected with myxoma virus is encoded by the M-T7 open reading frame. This protein has significant sequence similarity to the human and mouse receptors for interferon-gamma (IFN-gamma). Furthermore, the myxoma M-T7 protein specifically binds rabbit IFN-gamma and inhibits the biological activity of extracellular IFN-gamma, one of the key regulatory cytokines in the host immune response against viral infections.

B cell sensitivity to IgE-suppressive activity of IFN-gamma is polymorphic and controlled by a non-H-2-linked gene

It has been suggested that at least two distinct genetic factors are involved in developing atopic diseases. One is the major histocompatibility complex which controls antigen-specific polymorphism of IgE antibody responses and the other is an unidentified factor(s) which controls isotype selection, i.e., class switching to IgE. It is conceivable that both expression of and sensitivity to lymphokines that play central roles in controlling IgE biosynthesis may be involved in the latter polymorphism. To explore this possibility, we have examined the sensitivities of several mouse strains to interleukin (IL)-4 and interferon-gamma (IFN-gamma). The results show that (1) the sensitivity to IgE-suppressive activity of IFN-gamma, but not to the IgE-enhancing activity of IL-4, is polymorphic (e.g., C57BL/6 is 8- to 16-fold more sensitive than BALB/c to IFN-gamma); (2) F1 of these two strains (CByB6F1) are BALB/c type and H-2 congenic mice of d haplotype with B6 background are C57BL/6 type, suggesting that low sensitivity is a non-H-2-linked dominant trait; (3) the polymorphism is determined at B cell levels; and (4) sensitivity to IFN-gamma is not associated with mRNA expression of IFN-gamma receptors (R) by B cells. These data collectively indicate that BALB/c mice have a non-H-2-linked gene which decreases B cell sensitivity to IFN-gamma, but the gene effect is not associated with the expression of IFN-gamma R mRNA on B cells. The possible biological significance of the non-H-2-linked gene is discussed.

The structure and function of interferon-gamma receptors

Interferon-gamma exerts its pleiotropic immunomodulatory effects by interacting with a single type of IFN gamma receptor expressed on nearly all cells. Human and murine IFN gamma receptors have been purified, their cDNAs cloned and expressed, and their primary structure elucidated. In addition, a considerable amount of data is available that defines the life cycle of the receptor including the kinetics of its biosynthesis, its constitutive- and ligand-induced phosphorylation, and its recycling behavior. Recent transfection experiments have revealed that an additional species-specific component is necessary to form functionally active IFN gamma receptors in heterologous cells. On the basis of complementation assays, the gene for the human accessory molecule has been localized to human chromosome 21. However, the nature of the gene product(s) remains unknown. Using murine fibroblasts that contain a single copy of human chromosome 21 and eukaryotic cell expression vectors that contain a series of human IFN gamma receptor intracellular domain deletion mutants, we have been able to demonstrate that the receptor's intracellular domain plays an obligatory role in mediating IFN gamma-dependent biologic responses. Subsequent studies showed that two distinct regions of the intracellular domain are functionally important: a membrane proximal region of 48 amino acids needed for both internalization and induction of biologic responses and the carboxy terminal 39 amino acids needed only for function and not for internalization. Moreover, receptor-mediated ligand internalization was found to be insufficient for biologic response induction.(ABSTRACT TRUNCATED AT 250 WORDS)

Purification and biochemical characterization of a soluble mouse interferon-gamma receptor produced in insect cells

The extracellular domain of the mouse interferon gamma receptor comprising amino acids 17-243 of the protein was produced in Spodoptera frugiperda cells infected with a recombinant baculovirus. The receptor was mainly secreted into the culture medium and was purified to homogeneity in several hundred milligram amounts. The purification procedure involved four chromatography steps and delivered a soluble and active receptor with an overall recovery of 30%. From each purification run, two pools of soluble receptor with the same interferon gamma binding capacity were isolated. Under reducing electrophoretic conditions the protein of pool I migrates as two bands of molecular masses 32 and 34 kDa and of pool II as two bands of 30 and 32 kDa. The soluble receptor of both pools carries a heterogeneous glycosylation. After deglycosylation it appears as one protein band of 27 kDa. N-linked carbohydrates contribute about 6 kDa and O-linked carbohydrates 1 kDa to its molecular mass. The nonreduced protein specifically binds interferon gamma on ligand blots and in a solid-phase binding system and competes for the binding of radiolabeled interferon gamma to the cell surface receptor. The soluble mouse interferon gamma receptor exists as a monomer in physiological buffer and binds interferon gamma in its dimeric form. It is stable at room temperature and against tryptic digestion, but is very sensitive to proteinase K digestion. The soluble mouse interferon gamma receptor produced in the insect/baculovirus expression system may prove useful to study the function of interferon gamma receptor as an antagonist of endogenous interferon gamma in the treatment of immunological and inflammatory disorders.

Sequence similarity between opioid peptide precursors and DNA-binding proteins

The opioid peptide precursors, preprodynorphin and preproenkephalin show structure similarity with a transcription factor, hunchback and the putative helix-loop-helix DNA-binding proteins, lil-1, tal and twist. Segments with similarity contain the three enkephalin sequences in preprodynorphin and one in preproenkephalin which are present within heptapeptide repeats characteristic of an alpha-helical coiled-coil structure distinctive of an amphipathic helix-loop-helix DNA-binding motif. Hunchback and the opioid prohormones also have cystein-rich regions characteristic of zinc-finger domains in common.

Cytokines and their receptors

Cytokines act via receptor-mediated pathways to influence the regulation of both immune and non-immune cells. This review will discuss some of the most important developments over the past year which have contributed to the elucidation of the mechanisms of cell activation by these molecules.

The interferon-gamma receptor: a comparison with other cytokine receptors

During the past few years, identification of cytokine receptors has become a major goal in cytokine research. A great deal has been learned from the plethora of receptor structures that have been elucidated recently. Although, evidently, the complexity of the cytokine network extends to the signaling pathways involved, some of these pathways have now become more accessible. The challenge in the coming years will be to fill the gap between the receptors and the gene regulatory events induced by the various cytokines. Another challenge lies in the potential use of cytokine receptors as targets for modulating cytokine action. Since the topic of interferon (IFN) receptors has been reviewed recently, this minireview will focus on the current knowledge on the IFN-gamma receptor in the context of recent advances on other cytokine receptors. Some new receptor models that may be of consequence for characterizing IFN receptors will be presented briefly.

Molecular genetic markers spanning mouse chromosome 10

Somatic cell hybrids, recombinant inbred (RI) strains, and progeny of an intersubspecific backcross were typed by Southern blot analysis to prepare a linkage map of mouse chromosome 10. The seven genetic markers in this map, four of which had not previously been positioned, include genes involved in oncogenesis (Gli, Myb, Tra-1), proviral integration (Emv-25), and immune responses (Ifg, Ifgr, Pfp). The linkage map spans much of the chromosome and covers a region of the mouse genome with few molecular markers. The gene order established here demonstrates that the genes for murine interferon-gamma (Ifg) and its receptor (Ifgr) are at opposite ends of the chromosome and that Ifgr and the Myb oncogene are closely linked, a factor that may be related to their joint transcriptional enhancement in some plasmacytoid lymphosarcomas.