Inhibition of vesicular stomatitis virus-defective interfering particle synthesis by Shope fibroma virus

Potentiation by thyroxine of interferon-gamma-induced antiviral state requires PKA and PKC activities

Added to HeLa cells previously exposed to recombinant human interferon (IFN)-gamma for 20 h, thyroid hormone [L-thyroxine (T4)] in physiological concentrations potentiates the antiviral action of IFN-gamma by more than 100-fold in 4 h. We examined protein kinase activities for their contributions to the mechanism of this posttranslational effect of thyroid hormone. Added concurrently with thyroid hormone, the protein kinase C (PKC) inhibitor CGP-41251 (5 nM) blocked T4 potentiation of IFN-gamma action. Coincubated with CGP-41251, phorbol 12-myristate 13-acetate (PMA) reversed the effect of the inhibitor on thyroid hormone action. U-73122 (10 nM), a phospholipase C inhibitor, also blocked hormone potentiation. KT-5720 (500 nM), a protein kinase A (PKA) inhibitor, completely inhibited the T4 effect, whereas 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP) restored hormone action in the presence of KT-5720. In the absence of T4, 8-BrcAMP and PMA, added together to cells in the 4-h paradigm, fully reproduced hormone potentiation of the antiviral effect of IFN-gamma. Incubated individually with IFN-gamma-treated cells, the two agonists had no potentiating action. Thyroid hormone apparently must activate both PKA and PKC in the nongenomic pathway of IFN-gamma action to enhance antiviral activity in HeLa cells.

Production of human interferon-beta by Sendai virus and poly(rI).poly(rC): inhibition by neomycin

Neomycin inhibits the production of interferon-beta (IFN-beta) in human fibroblast cells in response to Sendai virus or to poly(rI).poly(rC) in a concentration-dependent manner, and to the greatest extent effective when added prior to or up to 2 h after induction. This inhibitory effect is negated when the protein kinase C activator, SC-9, is present during IFN-beta production in response to poly(rI).poly(rC), but not in response to Sendai virus. These results suggest that in human cells both virus and poly(rI).poly(rC) utilize an early neomycin-sensitive signal transduction step for the production of IFN-beta; because neomycin binds specific phosphatidylinositol phosphates, both of these inducers very likely require hydrolysis of these phosphates.

Effect of calmodulin antagonists on the interferon system: induction and action of interferons

Synthesis of interferon (IFN) in response to Sendai virus and the development of the resulting antiviral state were studied in human (BG-9) and murine (L-929) fibroblast cell cultures in the presence of the calmodulin antagonists, trifluoperazine (TFP) and N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7). Compared to control cultures, 16-fold and 8-fold more IFN was formed in human and murine cells, respectively, when 10 microM TFP was present in the medium for 24 h prior to IFN induction with Sendai virus. W-7 did not affect IFN production in human cells, but enhanced it in L-929 cells by 4- to 8-fold. TFP inhibited the antiviral state induced by homologous IFN in the two cell systems, and at 20 microM, there was a 3,000-fold increase in vesicular stomatitis virus (VSV) yield. It also reduced the maintenance of the antiviral state in human cells. In contrast, W-7 had no effect on the development of the antiviral state in either of the two cell systems. Thus, calcium-calmodulin dependent cellular processes are involved in both induction of IFN and its action. The several patterns response to TFP and W-7 may reflect different ligand-binding sites on calmodulin.

Calmodulin in interferon preparations: effect of interferon on calmodulin bioactivity

Heat-stable calmodulin immunoreactivity and bioactivity were detected in crude preparations of various types of human, murine and chicken interferons (IFNs). Calmodulin containing HuIFN-alpha was retained on a trifluorophenothiazine-Sepharose column. The two activities were separated by serial elutions with 50 microM Ca2+ (HuIFN-alpha) followed by 2 mM EGTA (calmodulin). While maintaining its full antiviral activity, calmodulin free HuIFN-alpha inhibited enhancement of Ca2+-ATPase activity in vitro by authentic purified eukaryote calmodulin. These results indicate that IFNs are calmodulin-binding proteins and that the secretion of both IFNs and calmodulin occurs from IFN-induced cells.

Characterization of lymphocyte interferons with different species specificities from normal and genetically dystrophic chickens

Lymphocytes from thymus and spleen of normal (Line 412) and genetically dystrophic (Line 413) chickens produce two types of interferons (IFNs) with different host cell specificities. The first type, referred to as ChIFN-alpha, demonstrates antiviral activity on primary normal chicken embryo (CE) cells. This activity is stable at 60 degrees C for 1 h and, in this respect, ChIFN-alpha is similar to the standard ChIFN-beta. In contrast, the second type, referred to as ChIFN-alpha 1, demonstrates antiviral activity in human and simian cells but not in primary CE cells. This activity is labile at 60 degrees C for 1 h. The amount of these two types of IFNs produced in lymphocytes from the spleen of dystrophic chickens was fourfold greater than that produced from normal chickens under similar experimental conditions. In contrast to the lymphocytes from thymus and spleen, the lymphocytes from the bursa of both the normal and dystrophic chickens produced only one type of IFN, namely ChIFN-alpha 1. The development of antiviral state in human cells by ChIFN-alpha 1 requires host RNA synthesis. Although ChIFN-alpha 1 has antiviral properties similar to HuIFN-alpha in human cells, the two IFNs are not antigenically related.

Persistent infection of Friend erythroleukemia cells with vaccinia virus

Cultures of murine Friend erythroleukemia (FL) cells, which are chronically infected with leukemia virus, were inoculated with vaccinia virus. The yield of vaccinia virus was determined by assaying plaque-forming units in mouse L2 cells, and the yield of leukemia virus was determined by measuring reverse transcriptase (RNA-dependent DNA nucleotidyltransferase) activity released into the culture fluid. Although no facilitation of one virus by the other was detected, persistently infected cultures were established. Electron microscopic examination revealed the presence of vaccinia and leukemia viruses in the same cell. The permanent lines of cells persistently infected with vaccinia were designated FLvac. Their morphology, growth rate, cloning efficiency, and ability to respond to the induction of erythrodifferentiation by treatment with dimethyl sulfoxide were not appreciably altered as compared to the parental FL cells. However, the persistently infected cells showed a marked decrease in tumorigenicity when assayed in DBA/2 mice. The infectious virus produced by FLvac cells and by L2 cells were indistinguishable as judged by restriction endonuclease patterns of virion DNA, structural proteins, and the activities of two virion-associated DNases. The yield of infectious vaccinia virus from FLvac cells generally declined after about 60 serial passages. Although some cell lines no longer yield infectious virus, they are resistant to challenge with vaccinia at concentrations that are cytolytic for L2 cells. The mechanism responsible for the establishment of the persistent infection remains unclear because defective particles, interferon production, and temperature-sensitive mutants have not been detected.

Interferon system of human cornea cells: interferon production, characterization, and development of antiviral state

The interferon (IFN) system of human cornea cells in culture was studied. IFN produced by these cells by infection with Newcastle disease virus (NDV) was shown, by neutralization studies with specific antisera against human alpha interferon (HuIFN-alpha) and human beta interferon (HuIFN-beta), to contain 90-95% antiviral activity characteristic of the HuIFN-beta and 5-10% that of HuIFN-alpha. The chromatographic behavior of human cornea IFN on Con A-Sepharose and zinc chelate agarose columns was identical to that of HuIFN-beta produced by human foreskin cells. The cornea cells developed marked resistance when exposed to either HuIFN-beta or human gamma interferon (HuIFN-gamma) against vesicular stomatitis virus (VSV), but to a much lesser degree against HSV-1. Both the laboratory-adapted strain and a clinical isolate of HSV-1 were found to be resistant to HuIFN-beta and HuIFN-gamma as compared with VSV. The clinical isolate of HSV-1 was, however, more sensitive to HuIFN-gamma than the laboratory-adapted strain. Furthermore, a combination of HuIFN-beta and HuIFN-gamma did not significantly increase the level of antiviral state induced in cornea cells against HSV-1. These results suggest that in-vitro culture of human cornea cells can be a valuable system to evaluate the potential of chemotherapeutic agents against common ophthalmic viral infections.