Inhibition of Murine Leukemia Virus Production in Chronically Infected AKR Cells: A Novel Effect of Interferon

Abstract

Treatment of AKR cells that had spontaneously become producers of a murine leukemia virus with a partially purified mouse interferon (> 5 X 107 international mouse reference units per mg of protein)inhibited endogenous virus production. This inhibitory effect decreased over a 72-hr period in a manner similar to interferon-induced antiviral activity diiected against vesicular stomatitis virus in AKR cells. Despite the inhibitory effect of interferon on infectious murine leukemia virus and viral reverse transcriptase (RNA-dependent DNA yqlymerase) titers in the culture fluids, intracellular levels of viral group-specific antigens were significantly increased. These results suggest that interferon treatment in AKR cells inhibited the assembly or release of the virus.Interferon is thought to inhibit virus replication by a complex mechanism. The optimal development of an intracellular antiviral state after interferon treatment takes several hours and is dependent on cell-directed RNA and protein synthesis. The existence' of this antiviral state gives rise to very few measurable changes in the metabolic qr physiologic state of the cells unless they are infected with an interferon-sensitive virus. In this case, the virus multiplies poorly compared to its replication in cells that had not been treated with interferon (1). Most reports suggest that the basis for this interferoninduced inhibition of-virus replication is an inhibition of the transcription or translation of virus genetic information (2,3). RNA tumor viruses are known to be sensitive to interferon (4). During a series of studies on the effect of interferon on the replication of mouse leukemia viruses, however, we made the unexpected observation that interferon treatment markedly inhibited the replication of a murine leukemia virus (MLV) in AKR cells that spontaneously had become chronically infected by an endogenous .MLV several cell generations before the interferon treatment. In addition, this inhibitory effect did not appear to be the direct result of an inhibition of the translation of virus genetic information, since the intracellular level of viral group-specific (gs) antigens was increased in cells in which the release of infectious virus and of viral reverse transcriptase were inhibited. MATERIALS AND METHODSThe AKR cells (here termed AKR,C-)' were supplied by Dr. W. Rowe. These were originally negative for virus production and negative for viral p30 (gs) antigen, and their culture fluids were negative for viral reverse transcriptase activity. These AKR,C-cells do, however, contain the AKR-murine sarcoma virus genome (5). The cells (now termed AKR,C+) spontaneously became virus producers, and more than 85%owere then positive for the virus group-specific antigens (gs-1 and gs-3) in an immunofluorescence assay. Type-C budding virus was easily detected when these cultures were examined by electron microscopy, and high titers of virus reverse transcriptase activity were found in AKR,C+ culture fluids (Table 1).The interferon used was prepared by ...

Effect of Interferon on Mouse Cells Chronically Infected with Murine Leukaemia Virus: Kinetic Studies on Virus Production and Virus RNA Synthesis

“…A similar effect of IF was observed when measured in terms of reverse transcriptase, infectivity or physical virus particles. This finding is consistent with that of Friedman & Ramseur (1974). However, Pitha et aL (i 976) found IF had a much greater effect on the infectivity of the released virions than on their reverse transcriptase activity.…”

Interferon Induces the Production of Membrane Protein-deficient and Infectivity-defective Vesicular Stomatitis Virions through Interference in the Virion Assembly Process

“…Interferon (IFN) inhibits murine leukaemia viruses (MuLV) at a late step in the virus productive process (Billiau et al, 1974;Friedman & Ramseur, 1974;Pitha et al, 1976;Billiau et al, 1975), while translation of virus proteins is apparently not affected. The inhibitory effect of IFN on these viruses can be expressed in one of two ways: (i) IFN caused a drastic reduction in the release of the virus particles from the cell membrane (Billiau et aL 1974;Friedman et al, 1975;Chang et al, 1977Chang et al, , 1978 and the budding virions were found to accumulate on the plasma membrane surface (Chang et al, 1977); or (ii) the effect of IFN was expressed as a dramatic reduction of the infectivity of the progeny virions, while the number of virions produced was only marginally reduced (Pitha et al, 1976;Wong et al, 1977).…”

Physical, morphological, and biochemical alterations in the membrane of AKR mouse cells after interferon treatment.

“…Based on the results of previous studies, several laboratories have suggested that interferon treatment inhibits murine leukemia virus at a late stage(s) in virus replication (5)(6)(7)(8)(9)(10)(11). In view of the relationship between glycoproteins and intramembranous particles, the block of virus production by interferon may involve an alteration of membrane-associated glycoproteins.…”

“…These changes could have been due either to interferon-induced alterations in the plasma membrane or to competition between interferon and the other ligands for a common binding site. In addition, interferon treatment of cells infected with RNA tumor viruses caused an unusual inhibition, which may be related to interferon-induced changes in the plasma membrane. In some systems, murine leukemia virus appeared to accumulate at the surface of interferon-treated cells (5,6); This resulted in a decreased production of the virus and an increase in the intracellular concentration of viral p30 antigen (7,8). In other systems, virus particle production in interferon-treated cells was quite close to that in untreated cells, but the infectivity of the particles was markedly decreased (9)(10)(11).…”

“…AKR,C-(AKR-2B), a mouse embryo cell line kindly provided by W. P. Rowe (National Institute of Allergy and Infectious Diseases), was grown in monolayers on McCoy's modified 5a medium (Grand Island Biological Co., Grand Island, NY) supplemented with 10% heat inactivated fetal calf serum (GIBCO), gentamycin (50 ,g/ml), streptomycin (100 ,gg/ml), penicillin (100 units/ml), and Fungizone (25 ,g/ml). Murine leukemia viral gs (p30) antigen and reverse transcriptase activity were not expressed in the cells or in their culture fluid (7,14). Ly cells were a strain of mouse cells originally obtained from J. Youngner, University of Pittsburgh, School of Medicine; these cells were grown in monolayers in Eagle's medium with 10% fetal calf serum (GIBCO).…”