Cell surface expression of murine, rat, and human Fc receptors by Xenopus oocytes

Interferon-gamma potentiates the antiviral activity and the expression of interferon-stimulated genes induced by interferon-alpha in U937 cells

Binding of type I interferon (IFN-alpha/beta) to specific receptors results in the rapid transcriptional activation, independent of protein synthesis, of IFN-alpha-stimulated genes (ISGs) in human fibroblasts and HeLa and Daudi cell lines. The binding of ISGF3 (IFN-stimulated gene factor 3) to the conserved IFN-stimulated response element (ISRE) results in transcriptional activation. This factor is composed of a DNA-binding protein (ISGF3 gamma), which normally is present in the cytoplasm, and other IFN-alpha-activated proteins which preexist as latent cytoplasmic precursors (ISGF3 alpha). We have found that ISG expression in the monocytic U937 cell line differs from most cell lines previously examined. U937 cells express both type I and type II IFN receptors, but only IFN-alpha is capable of inducing antiviral protection in these cells. Pretreatment with IFN-gamma potentiates the IFN-alpha-induced protection, but IFN-gamma alone does not have any antiviral activity. ISG15 mRNA accumulation in U937 cells is not detectable before 6 h of IFN-alpha treatment, peaks at 24 h, and requires protein synthesis. Although IFN-gamma alone does not induce ISG expression, IFN-gamma pretreatment markedly increases and hastens ISG expression and transcriptional induction. Nuclear extracts assayed for the presence of ISRE binding factors by electrophoretic mobility shift assays show that ISGF3 is induced by IFN-alpha within 6 h from undetectable basal levels in untreated U937 cells. Activation of ISGF3 alpha, the latent component of ISGF3, occurs rapidly. However, the increase in ISGF3 activity ultimately correlates with the accumulation of ISGF3 gamma induced by IFN-alpha or IFN-gamma.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased superoxide anion release by peritoneal macrophages in mice with a chronic infection of lactic dehydrogenase virus

The function of macrophages in mice chronically infected by lactic dehydrogenase virus (LDV) was studied. Superoxide anion (O2-) release was examined by using peritoneal macrophages. O2- release increased markedly from 3 weeks to 12 months, but not at 1 week post infection. O2- release was 1.2 to 1.5 times greater than in uninfected mice. Increased O2- release from macrophages in LDV-infected mice may explain, at least in part, suppressive effects on tumour growth seen in the chronic phase of infection.

Decrease in neutrophil migration induced by endotoxin and suppression of interleukin-1 production by macrophages in lactic dehydrogenase virus-infected mice

Neutrophil (PMN) migration into the peritoneal cavity after intraperitoneal injection of lipopolysaccharide (LPS), chemotactic activity of PMN, interleukin-1 (IL-1) production by macrophages (M phi) and its ability to attract PMN in mice chronically infected with lactic dehydrogenase virus (LDV) were compared with those in uninfected control mice. PMN migration into the peritoneal cavity decreased in infected mice when LPS was injected intraperitoneally. PMN chemotactic activity did not show any difference following infection. To assess the mechanism of this decreased PMN migration, IL-1 production, which is responsible for PMN attraction, was studied in LDV-infected mice. IL-1 production by M phi derived from infected mice decreased and its ability to attract PMN was weak. IL-1 production by M phi from control and infected mice increased after treatment by indomethacin and LPS. PMN migration into the peritoneal cavity increased after treatment with indomethacin and LPS in both control and infected mice. However, the rate of increase of IL-1 production and PMN migration was greater in infected mice. These results suggest that the excess activation of cyclo-oxygenase-derived products (prostaglandins) in infected mice might be responsible for the suppression of IL-1 production by M phi, resulting in decreased PMN migration induced by endotoxin.

Expression of the murine interleukin-5 receptor on Xenopus laevis oocytes

In this study we describe the use of Xenopus laevis oocytes for the detection of mRNA coding for a murine interleukin-5 (mI15) receptor. When injected with sucrose gradient fractionated polyA+ RNA derived from the murine 115-dependent pre B cell line B13, these oocytes could specifically bind 35S-methionine labeled mI15. A size of approximately 4000 nucleotides (25S) was estimated for the mRNA corresponding to the mIL5-binding activity. This binding was not blocked by a monoclonal antibody R52 specific for the MI15-receptor, suggesting that the oocytes express a different form of this receptor.

CD3 zeta subunit can substitute for the gamma subunit of Fc epsilon receptor type I in assembly and functional expression of the high-affinity IgE receptor: evidence for interreceptor complementation

The high-affinity receptor for IgE (Fc epsilon RI) is a four-subunit structure consisting of three distinct polypeptides: the IgE-binding alpha chain, the four-fold membrane-spanning beta chain, and the disulfide-linked gamma-gamma homodimer. cDNAs encoding each subunit have previously been isolated. Here we show that microinjection of Xenopus oocytes with a mixture of in vitro transcribed RNAs encoding each subunit results in expression of IgE receptors at the oocyte surface as detected by binding of IgE or anti-Fc epsilon RI alpha subunit monoclonal antibody to intact oocytes. Surface expression of Fc epsilon RI requires injection of all three subunits (alpha, beta, and gamma) RNAs. In particular, omission of Fc epsilon RI gamma RNA from the mixtures abolishes surface binding of either IgE or anti-Fc epsilon RI alpha monoclonal antibody to microinjected oocytes. However, addition of CD3 zeta RNA to Fc epsilon RI alpha and Fc epsilon RI beta RNAs restores IgE receptor surface expression when this combination is microinjected into oocytes. Metabolic labeling and immunoprecipitation of oocyte microinjected with a mixture of CD3 zeta plus Fc epsilon RI alpha and Fc epsilon RI beta RNAs reveals a noncovalent association between the CD3 zeta-zeta disulfide-linked homodimer and Fc epsilon RI alpha-beta. These results provide direct evidence for the functional relatedness of CD3 zeta and Fc epsilon RI gamma.

Angiotensin II-induced calcium mobilization in oocytes by signal transfer through gap junctions

Angiotensin II (AII) stimulates rapid increases in the concentration of cytosolic calcium in follicular oocytes from Xenopus laevis. This calcium response was not present in denuded oocytes, indicating that it is mediated by AII receptors on the adherent follicular cells. The endogenous AII receptors differed in their binding properties from mammalian AII receptors expressed on the oocyte surface after injection of rat adrenal messenger RNA. Also, the calcium responses to activation of the amphibian AII receptor, but not the expressed mammalian AII receptor, were blocked reversibly by octanol and intracellular acidification, treatments that inhibit cell coupling through gap junctions. In addition, AII increased the rate of progesterone-induced maturation. Thus, an AII-induced calcium-mobilizing signal is transferred from follicle cells to the oocyte through gap junctions and may play a physiological role in oocyte maturation.

Regulation of macrophage growth and antiviral activity by interferon-gamma

Interferons, in addition to their antiviral activity, induce a multiplicity of effects on different cell types. Interferon (IFN)-gamma exerts a unique regulatory effect on cells of the mononuclear phagocyte lineage. To investigate whether the antiviral and antiproliferative effects of IFN-gamma in macrophages can be genetically dissociated, and whether IFN-alpha and IFN-gamma use the same cellular signals and/or effector mechanisms to achieve their biologic effects, we have derived a series of somatic cell genetic variants resistant to the antiproliferative and/or antiviral activities of IFN-gamma. Two different classes of variants were found: those resistant to the antiproliferative and antiviral effects of IFN-gamma against vesicular stomatitis virus (VSV) and those resistant to the antiproliferative effect, but protected against VSV and encephalomyocarditis virus (EMCV) lysis by IFN-gamma. In addition, a third class of mutants was obtained that was susceptible to the growth inhibitory activity, but resistant to the antiviral activity of IFN-gamma. Analysis of these mutants has provided several insights regarding the regulatory mechanisms of IFN-gamma and IFN-alpha on the murine macrophage cell lines. The antiproliferative activity of IFN-gamma on these cells, in contrast to that of IFN-alpha, is mediated by a cAMP-independent pathway. The antiproliferative and antiviral activities of IFN-gamma were genetically dissociated. Variants were obtained that are growth resistant but antivirally protected, or are growth inhibited but not antivirally protected against VSV or EMCV. The genetic analysis indicated that IFN-alpha and IFN-gamma regulate the induction of the dsRNA-dependent P1/eIF-2 alpha protein kinase and 2',5'-oligoadenylate synthetase enzymatic activities via different pathways. Finally, a unique macrophage mutant was obtained that was protected by IFN-gamma against infection by VSV, but not EMCV, suggesting that antiviral mechanisms involved in protection against these different types of RNA viruses must be distinct at some level.

Interferon-gamma-induced transcriptional activation is mediated by protein kinase C

Interferon-gamma (IFN-gamma) regulates a variety of biological functions and is the principal lymphokine known to activate macrophages. In studies of the molecular mechanisms by which these cells are regulated by IFN-gamma, the transcriptional activation of an IFN-gamma-inducible gene, gamma.1, in human macrophage-like cell lines was examined. Transcription of this gene is rapidly induced by 0.1-1 unit of IFN-gamma. In addition, gamma.1 transcription is efficiently induced by phorbol 12-myristate 13-acetate, which is known to activate protein kinase C (PKC). Both stimulators of gamma.1 transcription induce the translocation of PKC from the cytosol of a membrane fraction. Two selective inhibitors of PKC, H7 and sphingosine, suppressed not only the induction of gamma.1 mRNA but transcription of HLA-DR by IFN-gamma as well. These findings establish that PKC plays a significant role in the signal transduction pathway leading to transcriptional activation of some IFN-gamma-regulated genes of cells of the mononuclear phagocyte lineage.

cDNA cloning and primary structure of a white-face hornet venom allergen, antigen 5

A major allergen of white-face hornet (Dolichovespula maculata) venom is antigen 5 (also designated Dol m V). We have determined the primary structures of two forms of this protein by cDNA and protein sequencings. These two forms with 204 and 205 amino acid residues differ in 23% of their sequences but they are antigenically similar. Both forms have sequence similarity with a pathogenesis-related protein of tobacco leaf. In a 130-residue overlap of these proteins, 35-39 residues were identical. Hornet antigen 5 cDNAs were isolated from an expression library in lambda gt11 phage using antibody probes. Several of the cDNAs were not full length, but the fusion fragments expressed were immunoreactive. These results suggest that antigenic determinants of the sequential type are distributed throughout the entire molecule of antigen 5. After subcloning, antigen 5 was also expressed in pKK233-2 plasmid.

Expression of rat brain excitatory amino acid receptors in Xenopus oocytes

Xenopus laevis oocytes when injected with rat brain mRNA synthesize neuronal receptors that can be analyzed electrophysiologically. After a post-injection incubation period of 24-72 hours, L-glutamic acid, kainic acid and quisqualic acid caused a dose dependent (10-100 microM) depolarization of the oocyte membrane. The voltage and conductance changes associated with kainate activation were distinguishable from those seen for L-glutamate or quisqualate. There was no response to L-aspartate application and an inconsistent response to N-methyl-D-aspartate. Upon fractionation of the mRNA on sucrose gradients, transcripts greater than 2 Kb in length were obligatory for the synthesis of excitatory amino acid receptors. The electrophysiological response of injected oocytes exposed to L-glutamate was similar to that of native oocytes when exposed to muscarinic agents. This similarity may reflect the activation of the same ionophore and suggests that the active mRNA fraction for glutamate responsiveness either encodes for a binding protein that can be assembled along with native ion channels into the oocyte membrane or encodes for a glutamate binding site with a similar channel.

Structural heterogeneity and functional domains of murine immunoglobulin G Fc receptors

Binding of antibodies to effector cells by way of receptors to their constant regions (Fc receptors) is central to the pathway that leads to clearance of antigens by the immune system. The structure and function of this important class of receptors on immune cells is addressed through the molecular characterization of Fc receptors (FcR) specific for the murine immunoglobulin G isotype. Structural diversity is encoded by two genes that by alternative splicing result in expression of molecules with highly conserved extracellular domains and different transmembrane and intracytoplasmic domains. The proteins encoded by these genes are members of the immunoglobulin supergene family, most homologous to the major histocompatibility complex molecule E beta. Functional reconstitution of ligand binding by transfection of individual FcR genes demonstrates that the requirements for ligand binding are encoded in a single gene. These studies demonstrate the molecular basis for the functional heterogeneity of FcR's, accounting for the possible transduction of different signals in response to a single ligand.