Interferon induction by viruses and polynucleotides: a differential effect of comptothecin

Topoisomerase 1 inhibition suppresses inflammatory genes and protects from death by inflammation

The host innate immune response is the first line of defense against pathogens and is orchestrated by the concerted expression of genes induced by microbial stimuli. Deregulated expression of these genes is linked to the initiation and progression of diseases associated with exacerbated inflammation. We identified topoisomerase 1 (Top1) as a positive regulator of RNA polymerase II transcriptional activity at pathogen-induced genes. Depletion or chemical inhibition of Top1 suppresses the host response against influenza and Ebola viruses as well as bacterial products. Therapeutic pharmacological inhibition of Top1 protected mice from death in experimental models of lethal inflammation. Our results indicate that Top1 inhibition could be used as therapy against life-threatening infections characterized by an acutely exacerbated immune response.

A retrovirus-like strategy for expression of a fusion protein encoded by yeast transposon Ty1

Eukaryotic transposons such as the Ty element of yeast or the copia-like sequences of Drosophila show structural and functional similarities to both prokaryotic transposons and retroviral proviruses, but the prokaryotic transposons and retroviral proviruses use markedly different expression strategies which yield products having entirely different functions. To determine the phylogenetic relationship between eukaryotic transposons, prokaryotic transposons and retroviruses, we have sought to identify and characterize the proteins encoded by the yeast Ty element and to describe the strategies used to express these proteins. We show here that the yeast transposon produces a fusion protein by a specific frameshifting event that fuses two out-of-phase open reading frames (ORFs). The process is remarkably similar to that used by retroviruses such as Rous sarcoma virus (RSV) to produce Pr180gag-pol.

Factors affecting heterologous gene expression in Saccharomyces cerevisiae

The 'promoter' fragment from the yeast phosphoglycerate kinase (PGK) gene has been used to direct the expression of human interferon-alpha-2 (IFN alpha 2) on a high-copy-number plasmid in yeast. The yields of IFN alpha 2 are only 1-3% of yeast total protein, whereas the maximum yield of PGK produced by the PGK gene on a high-copy-number plasmid is at least 50%. IFN alpha 2 is turned over more rapidly than PGK but in addition a major reason for the relatively low level of IFN alpha 2 is that IFN-specific RNA levels are much lower. This does not reflect differences in plasmid copy number or integrity, or differences in the 5' and 3' untranslated regions of the transcripts or DNA flanking regions. It appears that the presence of heterologous coding sequences, or the absence of specific yeast sequences causes a reduction in heterologous RNA levels in yeast.

How useful are serum and CSF interferon levels as a rapid diagnostic aid in virus infections?

Specimens from a total of 162 patients were studied prospectively using a rapid nucleic acid synthesis inhibition assay and a plaque-reduction assay to detect interferon levels in serum and cerebrospinal fluid. The specificity, consistency, and diagnostic applications of the rapid assay were evaluated by intensively investigating each patient for possible viral illness. Forty-one percent of patients with proven acute virus infections (excluding those with acute hepatitis and infectious mononucleosis) had unequivocal detectable interferon in serum or cerebrospinal fluid, compared with only two patients with bacterial infections (7%) who had equivocal interferon in the serum. Retrospective analysis showed the test to have high specificity for virus infections, but in patients with clinical syndromes of uncertain aetiology the test was not a particularly sensitive indicator of the presence of subsequently detected virus. The presence of interferon was not related to the time during the illness at which the sample was taken, nor to the numbers of lymphocytes in the cerebrospinal fluid, nor to the patients' general symptoms.

Secretion of a macrophage-activating factor distinct from interferon-gamma by human T cell clones

Supernatants from clones of human T lymphocytes that were responding to a purified Mycobacterium tuberculosis antigen were able to activate macrophages and macrophage-like myeloma cells (U937) to release increased amounts of the microbicidal agent hydrogen peroxide. The activity was not neutralized by monoclonal antibody against interferon-gamma (IFN-gamma), was greater than could be accounted for by the IFN-gamma activity in the supernatants, and was separated from IFN-gamma by high performance liquid chromatography. It is evident that IFN-gamma is not the only macrophage activator released by T lymphocytes responding to microbial antigen, and may not even be the main one to enhance antimicrobial activity in infections such as tuberculosis.

Differences in the expression of the human interferon-gamma gene in fresh lymphocytes and cultured lymphoblasts

Fresh human peripheral blood mononuclear lymphocytes and lymphoblasts that had been grown for a period in T-cell growth-factor containing medium were stimulated with staphylococcal enterotoxin A plus mezerein to produce interferon-gamma (IFN-gamma). Growing lymphoblasts produced peak levels of IFN-gamma much earlier after induction than fresh lymphocytes. Quantitation of the steady-state levels of IFN-gamma mRNA showed these to differ markedly between the two cell types over a period of time post-induction. In fresh lymphocytes the steady-state levels of IFN-gamma mRNA increased to a peak level over a period of 4 days while in growing lymphoblasts the peak level occurred after 8 hours. These differences in IFN-gamma mRNA production were shown to be not the result of gross alteration of RNA metabolism following blast transformation.

Expression of the human interferon-beta gene cloned in phage M13 mp7

The single-stranded DNA phage, M13 mp7 was used in the construction of an expression vector containing the coding sequence for mature interferon-beta (IFN-beta). Two clones expressed a fused polypeptide showing the biological and physicochemical properties of IFN-beta, despite the fact that the N-terminal amino acid sequence had been changed; 10(6) I.U./l of culture were produced with a molecular weight of 20 000.

Expression in Saccharomyces cerevisiae of human interferon-alpha directed by the TRP1 5' region

The complete 5' flanking region of the yeast TRP1 gene encoding N-(5'-phosphoribosyl)- anthranilate isomerase, a nonabundant protein, has been cloned and the nucleotide sequence data has been extended from -102 to -440. The CT block--CAAG structure common to all efficiently expressed yeast genes is altered in the 5' region of TRP1 and a sequence postulated to be involved in general amino acid regulation is absent. There are two possible TATA boxes at -224 and -262. TRP1, in common with HIS3, HIS4 and TRP5 has a region of dyad symmetry upstream of the coding sequence which may play a role in initiation of transcription. The relative efficiency of gene expression directed by the complete 5' TRP1 region was assessed by comparison with that of PGK by inserting a cDNA for a human interferon-alpha downstream of their respective 5' regions. The respective interferon yields indicate that their in vivo expression capabilities are a function of their 5' regions.

High-level expression of an interferon alpha 2 gene cloned in phage M13mp7 and subsequent purification with a monoclonal antibody

A cloned interferon alpha 2 (IFN-alpha 2) gene was partially digestd with Pvu II to give a fragment that was inserted into the HincII site of the lacZ gene of bacteriophage M13mp7. Two recombinant phages containing the IFN-alpha 2 sequences in the correct orientation for expression from the lac promoter were characterized in detail. DNA sequence analysis showed that the inserted IFN-alpha 2 gene was in phase with the initiation codon of the lacZ gene. The polypeptide product has an additional 19 amino amino acids at the amino terminus of the mature IFN-alpha 2. The first 11 amino acids originate from the amino terminus of beta-galactosidase, and the remaining 8 amino acids are part of the signal sequence of pre-IFN-alpha 2. Infection of Escherichia coli with these phage followed by induction of the lac promoter with isopropyl thiogalactoside gives high yields (up to 10(9) units/liter with an average of 1.5 X 10(8) units/liter) of the modified IFN-alpha 2. This was purified to homogeneity in a single step by immunochromatography using the monoclonal antibody NK2. The nonreduced product had an apparent molecular weight of 20,500 and was shown by immunoradiometric assay to have the same specific activity as IFN made in Namalwa cells. It exhibited the characteristic cross-species antiviral activity of IFN-alpha 2.

Production of human alpha- and beta- interferons by human-rodent hybrids

Attempts were made to demonstrate human alpha interferon production in virally induced human-rodent cell hybrids. In all hybrids investigated human beta-interferon production was detected when the relevant human chromosomes were retained, but only low levels of human alpha interferon could ever be detected even when human chromosome 9, which contains at least eight alpha-interferon genes, was present in the hybrid. The detection of human alpha interferon was made possible only by the use of specific antisera to human alpha and beta interferon and the sensitive virus yield-inhibition assay. Evidence is presented for independent regulatory mechanisms governing the expression of human alpha and beta interferons in human-rodent hybrids.

Toxicity of interferon

The effects of partially purified human leucocyte interferon (PIF) and of a preparation purified by passage twice through a monoclonal antibody affinity chromatography column (NK21F) were compared with those of a control solution in healhty volunteers. After intramuscular injections both interferon preparations caused rises in pulse rate and body temperature, changes in circulating white cell counts, and various unpleasant symptoms, the most common of which were headache, malaise, and fever. Slightly lower doses of NK21F were given, and this was reflected in lower peak serum concentrations. Mean symptom scores, however, were not lower after NK21F than after PIF. Local inflammatory reactions eight hours after intradermal inoculations of these interferons were similar. Purification of interferon using a monoclonal antibody does not reduce the facets of its activity considered in this study. They are therefore inherent in the leucocyte interferon type selected by the antibody.

A monoclonal antibody for large-scale purification of human leukocyte interferon

A clone of hybrid myelomas (NK2), secreting a mouse monoclonal antibody to human leukocyte interferon, has been isolated. The antibody neutralizes the antiviral activity of the interferon and, when covalently attached to a solid support and used as an immunoadsorbent, allows interferon purification of up to 5,000-fold in a single step.

Interferon induction with Newcastle disease virus in FS-4 cells: effect of 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB)

DRB is an inhibitor of heterogeneous nuclear RNA (hnRNA) and messenger RNA (MRNA) synthesis. The effect of DRB on interferon production stimulated by Newcastle disease virus (NDV) in the human FS-4 cells was studied. Interferon production in cells primed by treatment with interferon was markedly enhanced (superinduced) in the presence of DRB. This superinduction was essentially due to an inhibition of the rapid decline (shutoff) of interferon production observed in primed cells not treated with DRB. Continuous presence of DRB was required for maximal superinduction. In this and other respects the interferon response induced by NDV in primed cells resembled poly(I). poly(C)-induced interferon production. In contrast interferon production in cells not primed with interferon was virtually abolished by DRB treatment. Since neither virus specific RNA synthesis nor virus replication were significantly affected by DRB, the inhibition of interferon production is likely to result from the inhibitory action of DRB on a cellular, rather than viral, function. Apparently some differences exist in the synthesis or processing of the mRNAs for interferons in primed and unprimed cells and these determine the different sensitivities of these two responses to DRB.

The binding of poly(rI) - poly(rC) to human fibroblasts and the induction of interferon

Human embryonic fibroblasts produce interferon when incubated at 37 degrees C after being treated at 4 degrees C with poly(rI) - poly(rC), either by addition of the double-stranded duplex or by sequential addition of the constitutent single-stranded polynucleotides. Cells which have been incubated with double-stranded poly(rI) - poly(rC) can be prevented from forming interferon by washing the cells with high concentrations of salt, immediately after adsorption of polynucleotides, or by incubation of the cells with single-stranded polynucleotides. The inhibition is probably due to displacement of the inducing molecule from the cell surface. Interferon production by cells treated sequentially with poly(rI) and poly(rC) is not inhibited by either of these treatments and the polynucleotides are not easily displaced from the cell surface.