The mechanism of action of interferon

2',5'-oligoadenylates inhibit relaxation of supercoiled DNA by calf thymus DNA topoisomerase I

DNA topoisomerases interconvert various topological isomers of DNA and play key roles in replication and gene expression. The possible involvement of the 2',5'-oligoadenylates (2-5A) system in cell growth, regulation, and cell differentiation led us to investigate the effects of 2-5A on mammalian topoisomerases. We found that the calf thymus type I topoisomerase was inhibited by a variety of 2-5A compounds. The level of inhibition was dependent upon the number of residues and the degree of phosphorylation at the 5' terminus. The 5'-triphosphorylated 2',5' hexamer, ppp(Ap)5A, was the most effective, strongly reducing relaxation at less than micromolar concentrations. These results raise the possibility that physiological concentrations of 2-5A of sufficient chain length may be capable of regulating gene expression by virtue of a direct inhibition of DNA topoisomerase I.

Interferon-mediated inhibition of prostaglandin synthesis in human mononuclear leukocytes

In this study, the question of whether human leukocyte-derived and fibroblast-derived interferon had an effect on prostaglandin metabolism in human peripheral blood mononuclear cells has been considered. Both leukocyte- and fibroblast-derived interferon were potent inhibitors of mononuclear cell prostaglandin synthesis at low physiological concentrations. Inhibition required a minimum incubation of 1 hr. Interferon had no effect on release of arachidonic acid; synthesis of hydroxy fatty acids was slightly increased.

Clustering of leukocyte and fibroblast interferon genes of human chromosome 9

At least ten leukocyte interferon genes and the single known fibroblast interferon gene have been localized on the pter leads to q12 region of human chromosome 9. Gene mapping was accomplished by blot hybridization of cloned interferon complementary DNA to DNA from human-mouse cell hybrids with a translocation involving human chromosome 9. Supporting evidence suggests these genes are clustered.

Poly(A):poly(U); poly(O8A):poly(U); poly(A):poly(MeNH5U) and poly(O8A):poly(MeNH5U) versus Bida Semliki forest virus in chick embryos

Poly(A):poly(U) (polyadenylic acid:polyuridylic acid hybrid); poly(O8A):poly(U) (poly-8-oxy-adenylic acid:polyuridylic acid hybrid); poly(A):poly(MeNH5U) (polyadenylic acid-5-methylamino uridylic acid hybrid) and poly(O8A):poly(MeNH5U) (poly-8-oxyadenylic acid:poly-5-methylamino uridylic acid hybrid) were studied in chick embryos to compare the protection offered against Semliki forest virus (the Nigerian strain) AN 49809. The modified polymers showed a higher activity index but were more toxic than the unmodified analogue.

Viral interference phenomena induced by foot-and-mouth disease temperature-sensitive mutants in bovine kidney cells

Cultures of bovine kidney (BK) cells infected with temperature-sensitive (ts) mutants of foot-and-mouth disease virus (FMDV) were incubated at 38.5 degrees C, a temperature nonpermissive for mutant virus growth and RNA synthesis. The cells were subsequently resistant to viral growth and RNA synthesis when superinfected with wild-type FMDV and with heterologous fowl plague virus. The extent of interference was proportional to the multiplicity of infection of the ts mutant. It increased with time elapsed between infection with mutant and challenge infection, becoming greater than 99 percent after 24 hours. Interference was not proportional to decreased levels of cellular protein synthesis. The interference could be produced in the presence of actinomycin D, and thus was apparently mostly caused by the ts mutant itself rather than by interferon. The interference could not be produced in other less susceptible cell lines. Supernatant fluids from the BK cells infected with ts mutant virus interfered with wild-type FMD viral growth and RNA synthesis in fresh BK cells, and also showed low levels of activity in a vesicular stomatitis virus-plaque reduction assay. The properties of the supernatant fluid-interfering agent resembled to some extent those of an interferon. The ts mutant-mediated interference factor was apparently not able to diffuse into the supernatant fluid.

A murine cell possessing a dominant mutation affecting the regulation of interferon production: characterization by intraspecific hybrids

Using intraspecific hybrids, we have demonstrated the dominant nature of two phenotypic markers present in a mutant mouse 3T6 cell line, designated 3T6-VrB2. These are, resistance to virus infection (Vr) and semiconstitutive synthesis of interferon (IFsc). Hybrids were formed by polyethylene glycol-mediated fusion between 3T6-VrB2, or its parent 3T6, and 2TG0-13, a triply marked derivative of mouse 3T3 cells. When tested for the Vr marker, 3T6-VrB2 X 2TG0-13 hybrid clones displayed a level of resistance to virus infection which was equal to or greater than that of 3T6-VrB2. Similarly, when tested for the IFsc marker, these hybrid clones were found to possess the capacity to confer an interferon-induced antiviral state in mouse L929 cells upon cocultivation. By comparison, clones derived from 3T6 X 2TG0-13 fusions produced high levels of virus and failed to confer an interferon-induced antiviral state in L929 cells.

Murine interferon system regulation: isolation and characterization of a mutant 3T6 cell engaged in the semiconstitutive synthesis of interferon

We describe the isolation and characterization of a virus-resistant mutant of murine 3T6 cells. The mutant, designated 3T6-VrB2, displays a high degree of resistance to infection by members of the toga-, rhabdo- and picornavirus classes. The level of this resistance to infection is similar to the parent 3T6 pretreated with approximately 100 lU/ml of interferon. Upon co-cultivation of 3T6-VrB2 cells with interferon-sensitive mouse cells, an antiviral state is induced in the latter cells as measured by a reduction of virus yield following infection. The nature of the induction is defined by a series of experiments using anti-mouse interferon antiserum. In the presence of this antiserum, the ability of the mutant to induce an antiviral state in interferon-sensitive mouse cells upon co-cultivation is eliminated. Additionally, growth of the mutant cells in the presence of this antiserum causes a reversal of the virus-resistant phenotype. Our results indicate that 3T6-VrB2 contains a mutation affecting the regulation of the murine interferon system such that the cell is engaged in the semiconstitutive synthesis of interferon.